I agree, all of this could be a factor. I do disagree not to stretch hamstrings though but without an assessment of asymmetries, it's hard to tell. Piraformis is big factor when it comes to hamstring tightness as IT. To address any asymmetries, before they train with us we screen on the FMS, we found it a solid way of detecting any asymmetries and helps us design the program. Bottomline, tons of soft-tissue work.