have u tried it with the light in there? seems like the light would be to heavy for the plumber tape to keep the light from just laying on the bottom of the bake around.
and its hard to see from the pic but it looks like youve put tape on top of the cool tube to direct the light better. is that what youve done?
It would definitely help you avoid hot-spots, the diffusion of light will be more even if you paint it. Personally I would leave it clear and use a wider reflector