Hi Mirjam.
When I make flap-gusset socks I use half the total sock stitches to make the heels. I do generally make a "square" or "dutch" heel and not a half-hankie or V-heel. The square heel fits me better, especially when I leave 25% plus two stitches alone as the back of the heel and turn the heel on the remaining stitches. This has more to do with the nature of the heel itself, the height of my instep and the width of the back of my heel than with the size of the sock.
My short row heeled-socks are a different critter altogether. If I make the heel on 50% of stitches the instep is too short and the socks ride down in my shoes. When I make the heel on 60% of stitches the instep is deeper, the heel fits well, and the socks don't ride down.
I certainly don't know everything there is to know about knitting, but I do know that fiddling with the numbers often produces a better fit, no matter what the FO is supposed to be :D