What causes "cupped hands"?

I like Tim's suggestion re setting up an equi-tri first.
I also found that 5" midranges USUALLY sound "cuppier" than 6-7" midranges, all other things being equal. Something to do with 2-pi/4-pi stuff and resultant non-linearities with cabinet edge-diffraction. Found Aeriels to sound that way, as well that otherwise-nice Linn 3-way 5176 (?).
I found the Revel F30 and especially the Verity Audio Fidelio and Parsifals to NOT exhibit this 5" mid cuppiness, however. Somehow 6.5" 2-ways sound more easily "open", and are thus more forgiving of room setups.
Keep trying, and good luck.

I'll further add that I 've found that the cuppiness relates to a mild peak around 800-1k with 5" drivers. Similar peaks around 600Hz with 6.5- 7" mids CAN sound flatter. It's part of the reason designing (and integrating) a GREAT 3-way with a 5" is so tricky, and why 6.5-7" 2-ways are easier to live with. I tried in vain to voice a 3-way design of mine, but couldn't successfully get rid of that "pinched" peak at 800-1k with a nice Seas 5 that was otherwise super-smooth.
Bur Revel did get it right for $3500 with the F30, and of course the Verity Audio Parsifal is absolutely revelatory at $10k+.

Well, being from the northern clime, I know that the family jewels often tend to get frosty below the freezing mark, Hence the "cupped hands" to warm the jewels syndrome. I've heard that a good cable burner, or torch welder may help this problem too, but one should exercise caution with both methods.
good luck,
jb