Do you have a digital crossover that can do delays? With the midtops way in the back and the subs in the front, there would be wavefront smearing issues almost no matter where you were standing. The subs and the midtops would be out of phase unless you delayed the midtops and you were standing behind both the subs and the midtops. There would be hotspots, and null zones (in your case, a null in the center of room -
where you WANT the bass) where the speakers canceled around crossover. It's best to have sound radiating from one vertical plane (best to have it at one POINT, but that's not really possible). If you can't physically put all the radiating elements of the speakers on the same plane, you have to apply delay compensation to all the speakers physically ahead of speakers that are placed further back, to create a wavefront that is all on one plane. In your example, you've just got a big mess in terms of phase that can't be cured with delays.
Edit: also, check your wiring to MAKE SURE everything is wired with the correct polarity, and go ahead and try wiring the scoops in reverse polarity to see if that helps (after you put the midtops in the same wavefront plane!)
You always see scoop stacks in one huge wall of speakers - That's mainly because it works best that way. The horns couple together to produce an even wider mouth, which lowers extension and makes things a bit louder.
I'd try putting the scoops in a big line in the center, or two to a side, and the mid-tops ontop of the scoops and line up the cones of all the drivers vertically as best as you can. (if you can't, you need a digital crossover that can apply delays to the other speakers to bring further back speakers 'ahead' in time)
I'd start from there, and then start to worry about placement if my suggestion doesn't work at all (it may not). That's a fairly small looking room, and generally, horns like big rooms so I can only assume scoops do to some extent as well.
Edited by: bitcore