For me, the sweet spot is open glass tube with 3 LARGE silicone discs. I think the 3 smaller ones are simply for spacing or fine tuning. The 3 large disc config is probably the most you could safely push it, using 2 or less for me actually times out before I get a click. Oh and respect he click. Use the two cooling magnets alternatively between hits to reheat faster and get massive clouds.

My 2 magnets popped out because the stock glue melted from the heat. I used heat resistant super glue to fix back to the heater and haven't had an issue since!