Well first of all, you are a true sweetheart to knit all those socks for your pop (dad or granddad?)
Secondly, there are no rules when knitting something yourself (or someone you love). So I say if you like it, go for it.
Thirdly, I've always assumed that the heel flap was where it was because most socks go inside shoes, and the heel gets a lot of wear and tear against the back of the shoe. BUT, if you're making bed socks that will not be going into shoes, the sturdiest part should be the sole... so you sound like you're right on target!