Do not uproot your heels.
Any movement which would necessitate lifting the rear heel is
Any range of movement is acceptable, so long as the rear heel remains rooted to the ground.
This is simple, but many people never notice their inattentiveness taking over and it takes Intention to truly benefit from TaiChi.
If you know you are making mistakes in your Practice, then it is a guarantee that you are making progress.
*I don’t like that phrase, but it is very popular.