Distance

how far from top of canopy should a 900 watt led unit be in a space that's 2 1/2 feet by 3 feet. It's a closet lined with sun film.

Which 900w unit? If it's a commercial fixture 900 may not be the true watts. If it is 900 watts that would be way too much light for that space, but I'm guessing it's a Mars or Apollo?

Yes it's a Mars 2 900 watt. The closet is more like 3 x 4 feet. 12 feet high. I have a 800 cfm fan on a speed controller bringing in fresh air.

The Mars website says 24-30" above the canopy. Also says 90-120 degree optics so you can probably get it a bit closer than that. Sounds like you've got plenty of vertical space though, so just hang it where it gives the best spread for your space. Your area is close to the recommended so I would try it at 24" and see how it looks, and make adjustments if you think it will do any good.

The reason I'm asking is I'm not getting any stretch on new growth. Nodes are stacking a1/4 inch apart. I'm up around 30" now gonna see if there's any difference