preheating

I combine flushing and pre-heating, I put only a little water to do both, maybe about 2 oz? Then I swish that water around. I think it preheats the thicker base of pot enough and heats up the sides a bit. I would do this even if pre-heating did not make any difference, just to flush out dust get leaves to open up more if the tea is whole-leaf. I don't preheat the second, thin-walled glass pot where I pour tea after infusion. I would say that with thin glass pots this is completely unnecessary, with thicker glass pots I'd have to experiment but my guess would be it also makes little to no difference.