The inside of the ball valve also has a teflon seal in it, two actually. It will be to your benefit to fab a heat shield. Granted those teflon seals take a bunch of heat, but I have seen them deform enough to leak. The heat shield works bvecause it deflects heat and allows some dead space.
Take a hair dryer and hold it one inch from your hand, after your cuss and cool it off, do it again with a piece of foil in between, you will see what a little deflection and dead space can do for you.
Barry