First (and most obviously) make sure that you don't have the amp high crossed. Second - there is definitely some break-in time on the comps, but I will admit that I did notice some midbass right up front.
I am guessing that if it's in a small sealed box, you are just seeing too much acoustic suspension to allow any excursion. You might try pulling the driver out of the box, and driving it on a small amount of watts low-passed and see if it moves at all. I would also be willing to bet the amp is overrated by quite a bit and the set isn't getting enough power. Have you tested the amp with a DMM on a 1k sine-wave? Tried a 100 hz test tone?
Just throwing ideas out there, it's tough to tell what's going on without seeing it or knowing exactly what you mean by small. Mostly though, if the small boxes are fully sealed there is going to be a lot of compression-damping going on, the power handling of the mid is going to go up substantially and it's going to require more watts to get that low end movement going (which could be too much for the tweets so just be careful).
-FC