Could you upload a photo of such a problematic head?
Honestly, I don't understand your last post. I mean, the "shell" is a part of the drum, right? Is your problem, that there are uneven gaps between the drum's shell and the head's hoop (not talking about the DRUM's hoop / rim) when seating the head? How can you see that in a store without having your drum with you?
Unless your store received a load of heads with warped hoops, I'd still be interested in which combination of drums and heads have that problem.
If you have that problem with the same type of heads (e.g. two identical Remo Ambassadors), I'd think that your drums might be slightly oversized. In that case, something like a "Remo Classic Fit" might work better, but hard to tell right now.