If changing fit doesn't work, could be a tendon sheath or the tendon itself. If it's the sheath, ibuprofen will make the pain go away for a few hours. If that doesn't work, it's probably the tendon, though that seems unlikely, however the usual fix for that is heavy knee extension work, weight at the 4-5 rep limit. Over the years, I've kept various monsters at bay by doing sets of full depth squats with a 10-12 rep max once a week. So far, so good.

One of my mottos has been: don't try to fix pain with bike fit, fix it with bike fitness. Not to say that bike fit isn't important, but in my view it's more important for power and efficiency than anything else. That said, I usually start a fit with heel on pedal, then adjust for pull-back force at the bottom of the stroke. I never measure to get an initial fit, too many variables.