my Lynx flame is about 12-14" at max and I never run it that high. There is 24" between the tip of my torch and the back of the hood (stainless steel) and the wall is right behind.
This set up works even with Phantom outer ring flame, which is bigger and hotter and longer.
the picture below is with the inner fire (Lynx) as big as I can make it (on Oxycons).