There are many different takes on this.., the best, is to have a Teacher. other than that, I have found, in my experience, I have more duration when I use more upper lip. I can get an awesome sound when I use barely any upper lip, but it plays out in no time, and then I am just blowing air. Not to mention, it begins to hurt.., a lot!.
Everyone is different. Get a Teacher, if that does not work, try a different one, but at least look in a mirror, have someone else listen, and make some recordings, and check them periodically. Especially when you feel that you are not making any progress. This will help you continue, otherwise you may become discouraged.
Supposedly there are more muscle groups in the upper lip? That is why they suggest using more upper lip. There are good embouchure tips on Youtube. I like the one where you look in a mirror, to find your apperture. This was a big help for me. Instead of "Buzzing the lips" you just blow , and as the air seperates the lips, this is the "aperture" Center the mouthpiece there, and this is where you get the best "Clean" sound. (As long as your dental configuration allows it) Try not to use excessive pressure!