Vector Network: How to use "Mirror angle" only while dragging the handles? (not "Mirror angle and length")

Hello,

I’m using Vector Network to draw logos.
One small things I found is that, I cannot use “Mirror angle” only while dragging handles:

  • If I drag handles directly, it will automatically become “Mirror angle and length”
  • If I hold “Option” (“Alt”) and drag handles, it will become “No mirror”

I do want “Mirror angle” but not “length”. What should I do?