I would say yes, it is too much. I've read some members use a 10.0 in free ranging and placing them up at higher distances to avoid any issues. A more experienced member could give you a definite answer, this is just what I have read and learned.
People in France usually use 10.0. Here, i cheat because i have a UVB meter, so i can adapt my setups to pretty much anything i buy!
Basically, if your mesh is pretty dark and tightly sewn, i wouldn't see much problem, especially if your chameleon is over 6 months old and if he has room to go hide from the UVBs while still being able to bask to get hotter temperatures.
You can always higher your tube by 5 inches or so, and everything should be fine.