Social Distancing is NOT an Option

I am a few weeks into flower, at least for one of my two Autoflowers, day 36 from seedling to be exact. I am running two DWC 2 gal buckets filled to 1.5 gal under a 300W UFO LED light in a 2x2x4 grow tent. I suspected some light bleaching as shown in the picture below, so I moved the LED as high as I possibly could. I also lowered Potassium to the "Mid Bloom" ratio to discourage further veg growth.

My tallest colas are about 12" from the light. Should I expect to run into major space issues or have am I nearing my plants' final height? If growth continues, am I okay to run them up to 6"? Can increasing EC help calibrate light-nute balance and reduce light burn?

You have no issues with the light being to close IMO.

You are seeing the beginnings of a potassium deficiency IMO.

I would make sure you are using a good bloom feed around an EC of 2.0.

Try some defoliation in that room. I think it would help. Try snapping or bending some of the tops to keep the vertical height down. That's what I would usually do when rooms start to get out of control.