Thanks for the comments on the hip's relationship to PFSS. Comments help jog my brain, so do so frequently. SPG made a comment about placing the heels of the squatter on a barbell plate as a diagnostic tool. You would think that it would exacerbate symptoms, but not necessarily. If there is a deficit in dorsiflexion, the foot will bail out in the frontal or transverse plane, or both. Elevating the rear foot creates pseudo dorsiflexion during the squat, and will alleviate PF pain, if the TP or FP is creating the dysfunction. Of course, it is not a fix.
Oh, and thank you JH for mentioning the contribution of the contralateral hip to PFSS, and using a leg driver to sniff it out.
If you get a chance, take a look at the August issue of JOSPT. I will be commenting on the PFSS article.