i would stay 12 inches away at the least....put your hand under the light and move it up towards the light until you can feel the heat....im no expert, but if you only have 3' 4" to the light from the tote, im thinking maybe you would want to start the 12/12 flowering cycle at 12" tall...or 12" or so above the tote just to make sure you dont run out of room...some plants will double in size during the flowering process so you need to allow for it to gain some height during the 8-10 weeks that it needs to finish
I might add a little to this if you don't mind. As far as testing heat for light burn. I put my hand palm down at plant top. If I hold my hand there for 30 seconds or more and I feel heat but NOT discomfort the lights are good, OR you can move the lights lower
and try the test again. This method has worked well for me, but just remember, plants can really sprout suddenly in early flowering, if you go as close as you can, it can be a double edged sword if you are not dilligent in checking the "burn" height daily, especially the first two to three weeks of flowering.
The reason I do the palm down instead of up is I work with my hands lots, and my palms are less sensitive than the backs. Too much callous and scar tissue on my palms. If you have sissy hands then it doesn't matter.....lol.
As far as topping, I think I would suggest Uncle Bens' topping method (depending on how far along you are already....you want to catch it early for this to work fully) You could go with topping and side training/tying down as well, especially if too late for Uncle Bens' method. If you only have one plant, I would suggest trying to absolutely maximize your yield from that plant.
But side training and topping could work, you just might want to add a week or two, or even more if needed, to the veg time to maximize any changes you make.
Good luck
