I think stretching, more than any other thing in PE, has the potential to be either a waste of time or a total boon. I had to experiment with grip and etc.etc.etc. for a couple months before I really started to see a concrete effect from stretching. It is VERY DIFFICULT for me to get a good stretch using normal straight out, left, right methods.
Just about all of the stretching I do utilizes some kind of “fulcrum” type of stretch. By twisting my dick over my own hand, wrist, or a wooden dowel I find that I can really exert much more stress onto the ligs. Without using this kind of method it seems like I’m just constantly slipping on the skin. Try utilizing fulcrum style of effects if you’re also having a problem with grip. I also like to reach underneath my leg to grip my dick and then push down on my arm with my leg while slightly twisting the pecker to give a better grip. The key to stretching, as you’re deducing, is to really get a good stretch. It aint the easiest thing to do, but when you get it right it’s pretty obvious. Good luck.