While there are physical matters directly related to solid range production these concepts seem (to me) to be less relevant than the ATTITUDE the aspiring lead player has. To preface: I would bet good money that very few readers of this forum even have a solid High C to my satisfaction. Think this thought over for a minute. Very very few trumpet players have a solid, usable High C... OK now meditate on that for a few days and ask me for some suggestions. Wait here's one: Develop a powerful register up to High C with lots of endurance, THEN expand to High F.