All my tanks have nothing between the bulbs, distances ranging from 1 .1/2" to 4" and on my main tank 3'. As Daveedka said ,worry about the klutz factor, b/c I have actualy droped a whole light fitting turned on in the water while working on it, I got some DIY home electric shock treatmeat,LOL.
Then again used to pull all my powerheads out of the water by the cords until one of the cords pulled out of the powerhead, more DIY electric shock treatment,LOL.