JL, have you tried a ~1/5 load? I postulate that larger loads tweak the airflow dynamics a tad. Vapor takes longer to initially form with larger loads IME.
Or maybe I'm just really high like Vhole said.
Anybody try this...? For my first 3 hits (only works this many times), I trap the vapor in the HT by putting my thumb over the top and the bottom of the HT on my leg. So I get 2 hits of vapor for every 1 draw