I grow mine (the top leaves) within 1 inch of fluorescent lights (cool T-12 bulbs) and they do really well as long as the temperatures don't exceed 80-85 F range with heat from the lamps included. BUT if it's T5, then a more distant 5 inches sounds safer. Your plant looks very healthy right now. When they get a ton of light, and aren't fed very often, the leaves show some nice red coloration, which you can see in my sig pic. It seems that outdoors, they can handle the 80-85F temps a bit better.
Well, bloke, since you requested...
I just took some new pictures that I haven't been able to upload off my camera yet, but here's an oldie of a 'Big Easy' when I had time to feed it:
A month or so after this pic, the temps became to warm, and it formed its dormant bud.
After taking root cuttings for some people, and moving it to my cooler basement, the plant has grown well ever since.
However, I haven't had time to feed it since then, so the leaves only reach about 2.5 inches tall.
Feeding D. regia is required if you want to have the largest leaves possible. Once it doesn't get a meal for a while, it will slow down its growth and start producing smaller leaves.
As a side note, they produce an enormous root system, perfect for root cuttings, and repotting is extremely easy as long you don't break off most of the root system, and let them recouperate for a bit by placing them in dmimer light during that time, as well as making sure that the temperature does not get too high (which will kill them even if you aren't repotting them).
Also, Joseph Clemens has proven that leaf cuttings DO work, but obviously root cuttings are the fastest approach.