That wont be much good , as a T8 UVB tube is quite weak, even with a proper focusing reflector behind it or in a proper reflector hood...
See this for a comparison : viewtopic.php?f=34&t=235611
Buy a 24" T5ho 10%UVB or 12%UVB the same length and install in a reflector hood.
I agree. The Reptisun 10 tube bulbs that are the T8's are good but not real strong when
placed on top of a screen. Definitely try to get that mounted underneath of the screen
top so that the UVB can reach your dragon more effectively.
Good luck with your set up.