how about this – how did you test for IR? i have found that sometimes if you do the seated IR test, depending on how you sit (ie. pelvis position, posture), you may create more restrictions and it may show less IR.  there is also a lying version of it which may be better which leaves the leg more free to move and helps put the pelvis in a good position.

you lie down on your back, one leg extended. bring the other leg up to 90 deg at the hip and 90 deg at the knee and then do the IR test (you can do ER too of course). having someone else move the leg is better – you can stay relaxed and let them find the relaxed ROM versus you tensing to force your leg one way or the other. the extended leg helps keep the pelvis in correct position and there is no chair surface to restrict you.

have you tried that? i’m wondering if you may see a different result than with seated IR test.