Toe Up Socks - Help?

Has anyone used the toe-up instructions in the 12-stitch pattern section of SKS? I'm doing this for the fist time, and I am adding the instructions for the heel, flap, and gusset to a pair of socks that were written as top-down. The instructions are found on pages 59/60.

Hedgerow Socks (not an SKS pattern) knit toe-up

I'm not sure that the final fit will be correct, even though I've tried them on and it seems ok. My concern is that didn't have a point of refrence for how long I should have made the foot before starting the heel section. I'd love to hear about any experience others have had. These are to fit a size 10 1/2, and I started the heel after 8" of knitting on the foot.
Thanks for any guidance you can offer.