If being grown in a mild winter climate - like yours - double the size of the Bloodgood. 15 feet is a very conservatives estimate! It is one of the largest growing named forms of Japanese maples, similar to the species.

How the trees should be sited would depend on their form. If the BG branches low, I'd site the Waterfall at some distance. And for a better grouping, I'd include a third variety.

Photos of the area could help.

Here's the area as of Thursday:

I plan to put the Japanese maples near the circled X. Maybe a little closer to the fence, but that's the general area.

The garden is open to the South, there are wild trees to the West, and the house is on the East. So it's a part sun area, but with direct sun from around 11am until around 4pm.

There's a beech tree on the left (Northwest), circled in red. It'll grow and shade the rear part of the garden, but shouldn't affect the Japanese maples.

There's one impact sprinkler near the fence.

The bush that you see next to the fence has been replaced with a Major Wheeler.

My plan is to put patches of mondo grass along the front, followed by stepping stones, then fill in with flowers between the stepping stones and fence. The trees will be the centerpiece and focal point, though.

Here's my Waterfall, as of today:

I thought that I'd plant it and then wait a few weeks before cutting off the apparent dead limbs.

And for a better grouping, I'd include a third variety.

Considering that I'm not sure if my Waterfall will be stunted or if it will return to a Waterfall shape, what would you recommend as a third?