I know I probably went overboard, but I have been searching Houzz for shower/tub combos for myself if I decide to go in that direction. Most of these pictures have Master Bath titles - they tend to be small houses or apartments in large cities where space is an issue. They all have a generous sized tub. A few have extra shower bling and even a separate tub filler. All of them have material choices and the level of tile work that you see in a master bathroom. I'm sure that if I searched Houzz I could find just as many, or even more, remodels of small master baths where they have just built a walk in shower. I think the decision to do a shower/tub may be a personal choice because they want a soaking tub - since they are titled Master I'm assuming the bath is not the only bath in the house and they could easily just go with a shower. [[(https://www.houzz.com/photos/lakewood-bathroom-contemporary-bathroom-denver-phvw-vp~564696) [Contemporary Bathroom[(https://www.houzz.com/photos/contemporary-bathroom-ideas-phbr1-bp~t_712~s_2103) by Aurora General Contractors Heritage Home Improvement [[(https://www.houzz.com/photos/tamara-mack-design-interiors-traditional-bathroom-san-francisco-phvw-vp~1860108) [Transitional Bathroom[(https://www.houzz.com/photos/transitional-bathroom-ideas-phbr1-bp~t_712~s_2112) by San Francisco Interior Designers & Decorators Tamara Mack Design [[(https://www.houzz.com/photos/jackson-hole-residence-rustic-bathroom-portland-phvw-vp~1116073) [Rustic Bathroom[(https://www.houzz.com/photos/rustic-bathroom-ideas-phbr1-bp~t_712~s_2111) by Portland Architects & Designers Howells Architecture + Design, LLC [[(https://www.houzz.com/photos/bath-traditional-bathroom-charlotte-phvw-vp~1153799) [Traditional Bathroom[(https://www.houzz.com/photos/traditional-bathroom-ideas-phbr1-bp~t_712~s_2107) by Charlotte Architects & Designers Don Duffy Architecture [[(https://www.houzz.com/photos/tile-showers-traditional-bathroom-houston-phvw-vp~1597876) [Traditional Bathroom[(https://www.houzz.com/photos/traditional-bathroom-ideas-phbr1-bp~t_712~s_2107) by Lake Jackson Kitchen & Bath Remodelers JC Remodeling & Restoration, LLC [[(https://www.houzz.com/photos/icon-development-tofino-job-contemporary-bathroom-vancouver-phvw-vp~2443799) [Contemporary Bathroom[(https://www.houzz.com/photos/contemporary-bathroom-ideas-phbr1-bp~t_712~s_2103) by Nanaimo Tile, Stone & Countertops City Tile [[(https://www.houzz.com/photos/riverside-drive-super-groovy-masterpiece-contemporary-bathroom-new-york-phvw-vp~2456534) [Contemporary Bathroom[(https://www.houzz.com/photos/contemporary-bathroom-ideas-phbr1-bp~t_712~s_2103) by New York General Contractors Rusk Renovation [[(https://www.houzz.com/photos/burns-park-addition-and-remodeling-2000-and-2006-traditional-bathroom-detroit-phvw-vp~374078) [Traditional Bathroom[(https://www.houzz.com/photos/traditional-bathroom-ideas-phbr1-bp~t_712~s_2107) by Canton Architects & Designers Studio Z Architecture [[(https://www.houzz.com/photos/erica-islas-silverlake-contemporary-bathroom-los-angeles-phvw-vp~190979) [Contemporary Bathroom[(https://www.houzz.com/photos/contemporary-bathroom-ideas-phbr1-bp~t_712~s_2103) by Culver City Interior Designers & Decorators Erica Islas / EMI Interior Design, Inc. [[(https://www.houzz.com/photos/hall-bathroom-traditional-bathroom-new-york-phvw-vp~678390) [Traditional Bathroom[(https://www.houzz.com/photos/traditional-bathroom-ideas-phbr1-bp~t_712~s_2107) by New York Interior Designers & Decorators Nathan Cuttle Design [[(https://www.houzz.com/photos/master-bathroom-highrise-new-york-city-contemporary-bathroom-new-york-phvw-vp~89484) [Contemporary Bathroom[(https://www.houzz.com/photos/contemporary-bathroom-ideas-phbr1-bp~t_712~s_2103) by New York Photographers Vanni Archive/Architectural Photography [[(https://www.houzz.com/photos/carnegie-hill-residence-traditional-bathroom-new-york-phvw-vp~204853) [Traditional Bathroom[(https://www.houzz.com/photos/traditional-bathroom-ideas-phbr1-bp~t_712~s_2107) by New York Architects & Designers Incorporated[[(https://www.houzz.com/photos/upper-west-side-nyc-apartment-renovation-transitional-bathroom-new-york-phvw-vp~6968329) [Transitional Bathroom[(https://www.houzz.com/photos/transitional-bathroom-ideas-phbr1-bp~t_712~s_2112) by New York Architects & Designers John M Reimnitz Architect PC div> [[(https://www.houzz.com/photos/mediterranean-bathroom-mediterranean-bathroom-san-francisco-phvw-vp~1042841) [Mediterranean Bathroom[(https://www.houzz.com/photos/mediterranean-bathroom-ideas-phbr1-bp~t_712~s_2109) [[(https://www.houzz.com/photos/nyc-bathrooms-traditional-bathroom-phvw-vp~7215764) [Traditional Bathroom[(https://www.houzz.com/photos/traditional-bathroom-ideas-phbr1-bp~t_712~s_2107) by New York Design-Build Firms DELUXE Design & Construction [[(https://www.houzz.com/photos/cat-mountain-greenbelt-homes-austin-tx-transitional-bathroom-austin-phvw-vp~834553) [Eclectic Bathroom[(https://www.houzz.com/photos/eclectic-bathroom-ideas-phbr1-bp~t_712~s_2104) by Austin General Contractors Greenbelt Construction This post was edited by Anna_in_TX on Tue, Feb 11, 14 at 6:40

First thing I'd do is read the installation instructions to see what is specified there. If they recommend "X" number if vertical inches and you're less than that, or if you used PEX and they specify "no pex" or you used pex that has a smaller inside diameter than the recommended tubing, then essentially you have an installation issue. 1/2" pex does have a smaller inside diameter than 1/2" copper. For delivering water volume to a faucet it's normally not a problem, but when depending on a specified vertical water column, I guess the smaller diameter of the pex could be an issue. I'd call the manufacturer's tech support line and ask them about remediation. No harm no foul, it's best to run ideas past them before you crack open walls. You installed the shower head lower for the kids. Let's say you have yours 25" above the valve and the manufacturer specifies 30". What you could do is have the pipe come vertically out of the valve, and run it up the wall several inches higher than the shower head, say to 40", or even all the way to the top plate of the wall, then add a couple of 90's (to create and inverted "U") and then run it back down to the shower head. That would take care of the vertical issue while allowing you to still have a lowered shower head. If your pex to the tub spout is constricting flow out of the tub spout, that might need to be changed to a larger size of PEX or to copper. Something with a larger inside diameter. You're on your own well so it's likely excessive water pressure isn't an issue. What's on the "back" side of the wall that the valve and plumbing is installed in? Often times it's easier to cut through the back of the wall to access the plumbing, repair the plumbing, then TEST the plumbing, then patch the hole, than it is to access through the shower side of the wall.

Update: The position of the shower diverter valve appears to not be a causative factor. It was leaking again with the diverter set midway, and the faucet dripping slightly. Turning the knobs very hard to 100% off seems to have stopped it again. I'm still not clear on why there would be no leakage during a shower, even a long one, but there would be leakage from a very slight drip from the faucet. Is there some kind of weird backpressure issue that could cause this?

That is an incorrectly done project. You need an alcove tub with an integral tile flange to use as a tub shower. You then build up the end to be a bit higher ledge instead of a wall. The other 2 walls would fit flush over the tile flange.