It might be a bit confusing but, I have not read anything conflicting, lol!
The T5 HO is a 5/8 diameter bulb and is a lot stronger than the T8 which is 7/8 diameter bulb. This is why they take two totally different fixtures.
Distances vary because of the of uvb output strength:
10.0 T8......... Distance 6" to 8" to basking spot, for effect desired under the screen top (no obstruction)
10.0 T5 HO... Distance 12" to 18" to basking spot for desired effect.. Closer if above screen top 10" to 14"
I know its confusing cause it confused me for a while to, lol!