I'm not sure about the 10.0.....I have a 5.0, and that should be about 18 inches from the ground of the enclosure. You'll have to wait and see what some other forum friends say
I would look up the manual online for it if possible, as it will vary. This is very important as it can be dangerous if its too close, or not effective enough if too far away. Make sure the bulb is less than 6 months old, or it needs to be replaced anyways.