ok its great that you got the long tube UVB I was going to recommend you get one w/ the MVB here is some info on that MVB
100w version should be at around 12'' or so without any screen in front of it. Using a screen top, they should be maybe 8-10'' away or using the 160w versions should be around 14-16'' away through a screen. I don't have measurements from the output of the 160w versions, but I do have the 100w and can verify the outputs.
Now the T 8 is going to need to be unobstructed NO screen its not strong enough to go thru the screen are you using a Zoo Med Reptisun T 8?
Here is some stuff that works really good for hanging the fixture in side the tank
GE 15 ft. Cable Ties, Hook and Loop Spool, Black-10375 - The Home Depot
Its like a Velcro strap cut into strips and wrap around the fixture --- it needs to be directly above the basking decor approx 6-8 inches - how old is the dragon ? a year or older 95-100 baby 105-110 taken w/ a digital probe thermometer surface temps please