After all this "toe-up" sock knitting I have distilled the patterns I've been using (from Wendy Knits) into these generic instructions for turning the heel. Start turning the heel after having increased [8-10]/[12-14]/[16-18] gusset sts (for S/M/L size).
Mark the midpoint of the back of the sock.
K8 past the midpoint, KFB, K1, turn
YO, P8 past the midpoint, PFB, P1, turn
YO, K6 past midpoint, KFB, K1, turn
YO, P6 past midpoint, PFB, P1, turn
YO, P2 past midpoint, PFB, P1, turn
K across, knitting the YOs together with the st after them
repeat for 2nd sock (I'm doing 2 at once on magic loop)
knit across both insteps
Now place 2 markers, one at each side, to mark the width of the heel: count instep sts and divide by 2, count this number of sts on either side of the central marker and place another marker. You will have approximately [12-14]/[16-18]/[20-22] gusset sts on either side of these markers. Remove the center marker.
K, knitting each YO with the st BEFORE it, until you reach 1 st before the far marker.
Remove marker as you SSK and turn.
Sl 1, [P1, Sl1] to 1 before marker. Remove marker as you P2tog and turn.
K to 1 before the "gap", SSK, turn.
Sl 1, [P1, Sl1] to 1 before the "gap", P2Tog, turn.
Repeat until all gusset sts have been "eaten", ending with a K row.
Repeat for other sock.
Knit across both insteps.