This points pretty strongly towards ankle restriction. Basically, by putting your heels on the board you keep the ankle in a more plantar flexed (toes pointed) position than would be demanded if you were in a deep squat with your feet flat. You need more dorsilfexion, and you need it yesterday!

The bugger is that restrictions around the ankle, especially all that crummy calf meat, can take a fair amount of time and work to clear up. So if you’re going to take a stab at fixing this, make sure you consistently put in some quality mobility time until things are where you want them to be. You need to attack this thing from every angle: 

Joint Capsule / Muscle Dynamics / Soft Tissue Combo Episode

Soft Tissue: THE BONE SAW!!!