last part of single whip – back foot move ?

I have a question on the last part of single whip.
Just before the final stance, when the back foot turns in, the front of the foot is lifted and the turn-in is made on the heel.

Is it considered an error or a problem to make the turn on the ball of the foot while moving the heel back, as long as one is still moving energy up the leg?
I often find myself wanting a wider stance than I get when turning the foot in from the heel. If it is, then I’ll just have to try to step wider, but that feels awkward much of the time.

Thanks
Peter