I would suggest sewing something inside that area of the tights to protect them. From what you describe, I think the damage is being done from the inside - if I understand this correctly.
My bike shorts stay down on the prosthetic side when I wear them outside the suspension sleeve. I do often roll the sleeve up outside the shorts in warm weather, because it seems like a good idea to have that wicking material next to my skin. It feels cooler to me.
I tend to wear 1 or 2 layers of leg warmer on the non-prosthetic side. I do have some wind pants for really cold weather, and I use velcro or rubber band to make sure the excess leg fabric is bunched up away from the bike frame. I do have 1 pair of capris. I had a seamstress install a zipper in the leg on the prosthetic side, so that I could pull the capri leg up to do adjustments and sweat management.