I think it could be a camber, caster issue to fix it. BUT the reason is probably the XO point. I fixed quite a few by tipping them forward or backward. It is usually forward for a dip in the mids, and back if the tweeter is boiling my ears AND I want a little better Mid Bass response. Start with 1/2" and then go all the way down to shems. The chair idea is a good one to tune it the rest of the way..
Just remember, a little mojo goes a long ways.. Flat has never made me happy. It's always been a very slight frown, looking after tuning it the way I like it, I hear what I like.. Slight rise in the middle. When I measure (not to often) it's always the same.. a slight frown on the PEQ. 2 db rise is just about right..
Cup your ears and see if it's what you like (chair forward call or EQ it.)