Well... everyone will tell that I'm stupid and that it's not true... I'll talk with my own PC Grow experience. I'm starting my second grow now. My first grow is FULLY explained and pictured in my first thread. Anyway... From my experience in my PC Case, When the light was to close it seems like it was worst because of the heat build up. And because of the small space and reflective materials, I think it doesn't matters with the height of the light in there.
On my second grow, I'll leave my plants to the bottom and light high... cause it seems like because of the small enclosure, there was NO stretching at all!
Anyway, here are my threads if you want to look at:
First grow:
https://www.rollitup.org/indoor-growing/113971-my-pc-case-grow-box.html
Second grow(starting it almost same time as you):
https://www.rollitup.org/grow-journals/173437-computer-pc-case-grow-box.html
+REP