The rack slant mixer case I bought (C4UE-P-22) from EWI is a relatively new item (6months??), it's a full 22" deep so the LS9-16 fits nicely on the top rack rails. Deep enough that the XLR's on the back stay connected with just enough room for the lid. I have two Behringer ADA8000 in the rack spaces below, those XLR's stay connected as well.
The 22" depth makes all the difference. All my XLR's are straight, no issues on the front or back with this 22" depth.
EWI sells the same configuration with 18" depth, that model is more suited to a MixWizard size.
But can you apply the lid with XLRs patched into the LS-9?
I bought a couple of these a couple of years ago, and that is my only issue for LS-9 use.
BTW I think right angle XLRs solves it.
edited for typos ;-)