What I have noticed, with the tip of the tongue through the teeth and anchored to the front of the lower teeth, and a locked thick tongue with the top of the tongue pressed against the lower lip, upper lip, and top teeth, I can create enough compression to spit buzz the petal range though to high C. Adding mouthpiece to the buzz, I can fairly comfortably buzz to Eb above high C. Former student of Ralph Salamone and recently binging your and Rich Colquhoun's videos like crazy, as well as reading the ancient Callet forums on Trumpet Herald. I'm less than a week in as a comeback player and had a pretty solid high g about 15 years ago playing conventionally. My struggle seems to definitely be using way too much physical energy to build the compression. Your progress is encouraging to me, you sound fantastic!