I definitely would not have the Heresy,s sitting flat on the floor. Using a Heresy slant riser on them might work OK depending on the distance behind you. Also, an old trick from years ago would be to face them at the back wall or into the corners using the slant riser. Then the sound will reflect out above your ears. This works great when distance behind you is short. So many times it's difficult to get a perfect placement for the rear and generally requires some experimentation to get the best result. As far as using 5 Heresy's for your HT, absolutely do that. Take a look here,
http://www.avtruths.com/speaker.html