So from what I understand, the loop doesn’t move in a continuous, orderly fashion yes? It kind of doesn’t really have the correct form and is difficult to make the trip all the way up and over?
I’ve had problems with Kitty Nylons like that. Then I switched to Fat Kitty for a long while and now, when I came back to the nylons, I can do them just fine. It seems like I had the opposite problem as you do, but my suggestion, based on my own results, is to use the string that you can do it perfectly with every time and experiment on how to make the triangle bigger, WITHOUT PINCHING. Since you’re using a string that you’re comfortable performing Brent Stole with, you will subconsciously not worry about actually landing it, which will allow you to focus on making that end triangle as big as you can without pinching. Then, once you really know the movements of the string, you should be able to transition to any other string and replicate the results. Basically, you’ll be completely familiarizing yourself with each and every movement that goes into a Brent Stole, which should allow your hands to adapt to most new strings and be able to perform it the same way.
Keep in mind, these are my results and everyone is different. However, I think this method can be helpful to you, even if it doesn’t completely solve your problem; you’ll know the trick inside and out, regardless, and every bit of knowledge and experience helps.
Keep swinging your arm after you put your finger on the string, when I was learning this I noticed that I put my finger on the string and stopped swinging the string too early. You have to keep the motion and the range of the motion going longer than a normal laceration, that’s the key IMO
I’m not there yet, but I accidentally discovered that if I keep the extended NTH finger perfectly still, the loop is more likely to die. If I slide it outward (against the loop direction) just a little bit, it helps add extra momentum somehow. I’m sure a physicist could explain why.