Well, regarding reflections....there are a number of things that can be done...and experimentation will prove the fruitfulness of each.

Dash pads, underdash panels and transmission tunnel panels, aiming drivers in such a way that reflective surface influence is minimized.

I was thinking about building A-pillars from dense foam and wrapping them in a matching fabric and experimenting with shaped foam diffractors near the A-pillar tweet.

Some people (in 2-door coupes) have installed foam filled panels covering rear side windows.

But optimizing each enclosure to that specific driver and the frequncy range it is playing is critical...for instance I think it's unfair to expect a kickpanel mounted midbass to have low clean extention at high volumes to say 60 cycles in a small sealed enclosure...one thing I'm currently plotting is a resonance free "dead" enclosure for my 4-inch mid, it might involve a variety of techniques and materials, experimentation will undoubtedly bear some fruit here.

I too will try the two tweets unless I can get one set to sound right.