I joined this site just to answer OP's post.
I suffered from the exact same thing on steeper blues/blacks.. short, overturned heelside turns that ended in skidding. Your picture summed it up perfectly.
What helped me finally is that I realized I was opening my shoulders majorly before switching edges.. the steeper the hill the more I turned to face the fall line in advance of the turn.. trying to make my board swing around faster.
What finally fixed this was forcing my shoulders to stay parallel with my board and initiating the turn by flexing my front knee and using my ankles and feet to switch edges and start the turn with no upper body rotation. Its a little gnarly on a steep hill to flip to your downhill heelside edge with your back to the fall line, but once you prove to yourself it works, you get so much better turn shape and speed control.
Hope that helps!