I have been wondering the same thing about sciatic and pf., and have come to my own conclusion that for me, there seems to be a relationship. In fact, just this week I had a flare up of the pain in my right heel at the same time that I felt an ache in my sciatic. I've noticed that if I not only stretch my calf muscles, but also my hamstrings it helps with the added heel pain.
I notice an ache in the sciatic area sometimes from sitting too long at the computer. On those days, the ache seems to extend all the way down the back of the leg and into the heel, which then hurts worse than usual. On those days, I've copied my husband's hamstring stretches, which he does for his sciatic pain, and it does seem to relieve the added pain in the heel. I'm planning on making them a regular part of my stretching routine to see if they will help with my pf.
I'm so glad to have found this board as I've noticed many of you make the same observations as I have about the odd characteristics pf often exhibits.