Heel against rubber

[RKBUmp]

FED says on, or partially on and diagrams go on to show just a fraction of the heel on top of the plate.

ASA simply says in contact.

[clev1967]

Reason would be when you push off, your heel would then be in the air therefore pushing from a spot other than the "pitchers plate" (it will always be a rubber to me) which would also be illegal. My foot is bigger than most female pitchers but this would gain me 6 or 7 inches.