i also preheat my carb cap and bowl a bit before packing it up and smoking it, get way thicker vapour like this @ 610f but i dont like to toast my bud by letting them in the bowl, i find it taste less terpy... and i love that first hit super tasty hit...
and when i dont preheat the bowl, i tend to get uneven avb, i have a very large pulmonary capacity, i tend to extract most if not all of my bowl in one long draw, and if i dont preheat, the bottom avb is slightly greener than yellow brownish of a well extracted avb, but when i preheat the bowl, or im at my 3-4 consecutive hit, the avb is much more evenly extracted