I’ve always thought that heels being raised during a squat was more of a sign of inflexibility throughout the entire posterior, not just limited to the ankle.
This could very well be true. I have no evidence to back up my claim. Another thing ive noticed is these same people cannot stay upright at the bottom position. They tend to bend over from the waist. I don’t know if that would be attributed to poor posterior chain flexibility, poor core strength, or both.