Finger-scorch happens when:
-gaiwan is overfilled and tea is pooled around the edges of the lid and contacts your fingers
-the rim of the gaiwan bowl doesn't extend far enough outside the diameter of the lid, so the outer edge that you hold onto can't cool enough
-the knob of the gaiwan is too shallow or otherwise holds too much heat
-there is no base plate to grab, and the bottom rim is shallow & gets too hot
I've had to retire a few pretty nice gaiwans because they scorched fingers, but for reasons above, and not because they were glass vs porcelain vs heavier clay or stoneware.
BTW, this hold has saved my fingers when I do a lot of infusions close together and even my old-reliables threaten to scorch me: