When I read your post you talk about compact which takes folded and corner horns out of the picture. It sounds like the only part of the 3 way you are considering to go "horn" with is the midrange.

It's a little hard to picture what the system you are thinking about is like from what you've said so far but the compression driver midrange has a high efficiency. The other pieces you are using for top and bottom end should match fairly closely or you will just have to reduce the efficiency of the midrange.

Hope this helps.

Grant.