Is there a particular problem you're trying to avoid? Without knowing what exactly you're trying to accomplish with your model, it
would be safe to say that placing the H-stab on a level with the wing, or perhaps even slightly above would keep the stab slightly above the downwash created by the wing. In all honesty...I'm not even sure how much real "downwash" our models are creating. We're simply not displacing a lot of air molecules you know? Of course, a visit to the hobby shop, or the local airport would show that there are variety of wing/stab relationships in use...all work very well.

"Pitch neutrality" with flaps deployed most likely won't be possible unless some form of flap/elevator mix is used. If it were easy to achieve by a simple change to the stab position...Cessna, Piper, Beech, Mooney, Boeing and a host of others would have done it years ago.

Rolling your own models sure is a great way to enjoy the hobby...have fun with the project!

'Race