Trevor, a pivot is a form of added tension to one lip or another. There is a whole generation of players that used this. In many cases, the pivot had nothing to do with embouchure, it had to do with compensating for the natural tendency of trumpets to be flat in the upper register. Dave Monette goes into this in pretty great detail on his website. He also details that this is not necessary and what to do about it. Another way to compensate for bad playing habits is with tension in the upper body/throat, etc. Common practice with modern equipment is to absolutely minimize this. The pivot is no longer necessary to play in tune at the extremes. In this respect, hardware has gotten much better and can be played with less effort than many "vintage" combinations. As far as recommending a pivot or any other type of increased tension without working one on one with the player, the advice remains terrible. There is no reason to recommend tension to an unseen player regardless of the pro that may or may not use it. This is the problem with "internet advice". It can be easily taken out of context. Without the background, the fact that one player may use a pivot has maybe statistical significance, but is of no use out of the original context. Embouchure is in fact personal and there are a multitude of sins that are committed when we don't have the whole story. Trumpetlove is actually on a decent track with his teacher! The vizualisation of the open throat was the question and this is accomplished by taking BIG, RELAXED breaths. The most successful way that I teach this is to play long tones and slurs with no tonguing to get the sound started. I have described the circle of breath several times here at TM. Closed throat is upper body tension.