Ok so get some tin foil put it behind the bulb w/reflective side out--- what that does is reflect the rays downward to him which is what you want -- I would advise getting a new UVB fixture a 24" fixture like a Zoo Med or Sunblaster or Arcadia ---- here are some linksi've put it in the tank already. no it doesn't have reflector behind it but it wouldn't be difficult to add something that would be reflective
https://www.pangeareptile.com/store/zoo-med-reptisun-t5-ho-terrarium-hood.html you will need to order the 22" bulb Reptisun 10.0 T 5 it comes w/ a 5.0 which is similar to the one you have now a T 8 - you want the T 5 its a better bulb
or this one 24" https://www.pangeareptile.com/store/arcadia-prot5-uvb-kit.html they are out of stock of the bulb that comes w/ it but you can order it separately get the Arcadia 12% bulb these people are fast and good they ship Fed EX
or this https://www.amazon.com/Sunblaster-O...ocphy=9020114&hvtargid=pla-311792259791&psc=1 you want the 24" fixture w/ a Reptisun 10.0 T 5 bulb 22"
I would upgrade that UVB ASAP--- its going to benefit your dragon in the long run and less headache w/ the fixture your using now --- please let me know what your going to do