I can't do UWPS in the sixth string

Technique Critique
#1

At times I feel pain. I’ve been trying to do what Andy Wood does using this part of the hand as an anchor but I’m not sure I’ve got it

https://forum.troygrady.com/uploads/default/original/2X/f/f63448f464ed0ed65cd8bd5da545056976b3e78e.png