Well, from the perspective of sports fencing, one of the very first things a coach will force you to learn is to keep your heels grounded.

You could always tell who the new, inexperienced fencers were at my club by the fact that their back foot would be canted forward laterally, (a more natural, relaxed stance,) their knees weren't bent enough, and their back heel would start to float and hover.

Thankfully, I got my floating heel trained out of me after five years of brutal épée exercises, so my feet stay flat without any issue. (However; I did have to relearn the same thing with my opposite foot when I picked up HEMA. I never used my right foot like that in épée — it was always facing forward.)

In regards to HEMA; when I began to spar people who had only ever trained with other HEMA students/instructors, essentially all of them had hovering heels.

I know it's a different art, but all you need to do to get that heel flat, (which increases balance & the ability to advance/retreat more explosively,) is to make sure your heels are aligned, but your back foot is planted in an outward angle — as if you were trying to form an 'L' with the space between your feet. Also: get those knees bent!

I also highly recommend adding wall sits and squats to your exercise routines.

I know there's a lot of hate towards sports fencing, but damn if those folks don't have killer footwork. There are some things I learned as an épéeist that you really just can't get from a manuscript.