I think your question has more to do with the physics of heat than tea itself. The water hits the surface of the pot and the first surge of heat causes the surface to expand faster than the interior of the ceramic in the wall of the pot. To prevent this, you need to absorb the first jolt of heat. To do this, place a SILVER spoon (not stainless, etc.) in the pot and pour the hot water flowing over the spoon. I have used this method for years with no failure even on crystal tea pots.
