Don't take this the wrong way, but I think you have been lucky. The reason you are getting bite on the amsteel is because it's hollow braid. you are compacting the amsteel with your prusik, and the friction is able to hold you. if you constrict it to the point where there is no more give to the hollow braid, the prusik will slide. I don't know at what point the weight on the prusik will overcome the friction. It's definitely way less than say 6mm accessory cord on 10mm static double braid rope.
Here's a really bad analogy. If you were hanging over the side of a cliff, would you rather someone toss you the end of a piece of tubular webbing that's been filled with polyfil but the outside was coated in vaseline, or that same person toss you some regular old dry rope?
Tell you what. I have some, it's either 5/16ths or 1/4, amsteel laying around. I'm no professional, but PM me your address and I'll make you an amsteel whoopie sling to use as a bridge. you'll need to girth hitch one end and use a carabiner on the other. I don't want any $. Not even for shipping. I'm not so sure that even an amsteel whoppie sling is the safest bet for a bridge, but I think it's better than what you are currently doing. If I'm coming across as a jerk, I sincerely apologize. That's not my intent. Chances are you'll be fine doing what you're doing, but it's very little effort on my part, and I'd be glad to do it.
Here's a really bad analogy. If you were hanging over the side of a cliff, would you rather someone toss you the end of a piece of tubular webbing that's been filled with polyfil but the outside was coated in vaseline, or that same person toss you some regular old dry rope?
Tell you what. I have some, it's either 5/16ths or 1/4, amsteel laying around. I'm no professional, but PM me your address and I'll make you an amsteel whoopie sling to use as a bridge. you'll need to girth hitch one end and use a carabiner on the other. I don't want any $. Not even for shipping. I'm not so sure that even an amsteel whoppie sling is the safest bet for a bridge, but I think it's better than what you are currently doing. If I'm coming across as a jerk, I sincerely apologize. That's not my intent. Chances are you'll be fine doing what you're doing, but it's very little effort on my part, and I'd be glad to do it.