Hi,
Heel on the pedal locking out is pretty near, but I still lock out using the instep.
Ball of foot over the pedal or more I don't, so that is very near optimum.
Taking it easy on my folder I pedal with the ball behind the spindle.
If you radically change seat height you also need to look at handlebar fit.
I've found if you slightly lift off the seat with the pedals level, and your bum
doesn't move backwards or forwards, that is a good fit, but if it does move
then more likely your bars need adjusting and less likely the seat fore/aft.
rgds, sreten.