A few of you have contacted me with questions about where to start the heel. I realize that the starting point for the heel is probably a bit counter-intuitive, so here are some visuals.
If you are working a standard toe-up sock, this is probably the point where you would start working the gusset, and this is where you would start working the sole flap for JSPH.
The first picture shows where the sock would come to if unstretched. This is right at the top of the arch, where the foot circumference begins to increase. (Please forgive my black fingers... I'd just made myself a blueberry smoothie!)
The next picture shows where the sock should comfortably stretch to. This is about 1 inch of negative ease.
Here is a review shot, JSPH is on the right, standard square heel on the left. It might be hard to see the sole flap (blue) but the heel back (red) is right above it, so that shows you how long the sole flap is. See how, with JSPH, it reaches all the way to the middle of the arch.