In both form and function, piriformis resembles the
flying buttress of Gothic
cathedrals. The buttress takes lateral forces and helps convert them downward to the ground. It helps support and stabilize great weight with minimal material.

Let's make this graphic do double-duty. Chaitow (1996) takes four bony landmarks of the hip to help set up
coordinates for the green lines. From top left, the
landmarks are PSIS, ASIS, lower aspect of greater
trochanter, sit bone, and tip of coccyx.

These lines of force, so to speak, cross at the potential site of the central trigger point (pink) and satellite TP (yellow) of the piriformis.
Perhaps we've discovered
a new way of locating TPs, by analyzing where stress-lines cross?