I did something similar using the Hansgrohe 7" rainhead in my tub shower for my hall bath. I have a Greek tub, so it is only 4 feet long. I use it as a tub/shower and I did not want any glass. We put the rain head in the ceiling in the middle of the space, so it is 24" inches from the end of the tub. The water comes out a little bit on to the step in front of the tub, but not much. So if you did the 15" arm, you should be totally fine. You are right about the rainhead making much less of a mess. If you take a look at my pics under "pics of my new bathrooms" you will see that we have no glass doors or shower curtains in either shower (just a small panel next to the vanity in the master). We were able to do that because of the rain heads.

My rainhead is 86" off the floor, about 10" above my head and 25" above my wife's head. Good for both of us. I do have mine on a 9" straight arm, although 3" are in the ceiling leaving 6" exposed below the ceiling. Did a quick google and came up with this as the first hit, to be found at our favorite store. In your situation if having to go with the 6" or 12", I'd choose the 6". Mongo

Sorry, have been out of town and unable to respond. Thanks for your input. Babka, I was thinking that actuall hairwashing, etc. would be done with handheld and the rainshower would be used for a relaxing minute or two at the end, so not so much armwaving at that time. So splashing would just be whatever bounces off the body from a standing-still position. Still, there is some distance that is simple too close to the wall psychologically, but I'm not quite sure what that is! nycbluedevil, I'm glad to hear yours is working for you! Based on your response and photos, I've made myself a sketch of what I think you have. With the rainshower centered in a total length of 33" opening plus 36" pony wall, you have the center of the rainshower at 34 1/2 inches from the wall? Or did you subtract the 20" for the column before you centered the shower? That would put the center of it 24.5" from the wall. Would you mind measuring for me when you have a chance? Your example is the closest I've found. My husband originally specified 24" from the wall based on what felt comfortable, but we thought we could shrink it to as little as 20" if the overspray would be problematic. I think it wouldn't feel crowded if we were just standing there facing away from the wall... so glad to hear you don't have a splashing issue. We'll have waterproofing under the floor throughout and a bathmat at the opening to dry off on, but I don't want water on the front of the vanity outside the shower. We can also start with a glass panel and add a door if we need to as long as we have blocking there. I'd really rather not have a door. The floor will be heated, and I'm not too worried about it being cold. (The whole room is the size of some showers I see here!)

lanie, I'm in CT as well. I'm thinking that the pipe that will in the attic will be a section of pipe between the supply valve and the shower head? If so, simply pitch the horizontal run downwards, so it slopes downwards as the pipe gets close to the shower head. When you turn the water off, the pitch will cause the water to drain out of the horizontal run, there will be no water to freeze. What I would also do is go into the attic and use rigid foam insulation to create an insulated area in the joist bay in which the pipe will run. Make it look like an upside-down "U". The sides and top of the channel will be insulated from the attic. The open non-insulated bottom of the "U" will be against the bath ceiling, allowing heat from the bathroom to kep the pipe above freezing. PEX can still freeze, but its pliable enough to expand as the freezing water expands. Still, attach the PEX to a piece of 2x4 so it has no sags in it, or the sags may collect and hold water. Also, with the horizontal run of the being "open" at the shower head end, if residual water in the pipe were to freeze it should be able to expand without splitting the pipe. Mongo