Super Lumens last 2 weeks of flower

Running a Lumatek 600 watt with a hps bulb that's on it's second run. Air cooled hood, extractor fan and 5 or so other fans in room. Been dealing with temp issues. Now have it under control.Bumped the ballast up to super a couple days ago and my girls look happier already. Temps still running a bit high around 80 lights on. Question is they are about 18 in from lamp. Is that good? Or should I push it a bit and get them a bit closer over the next week or so?

Keep in mind light degrades thc, I use my super lumen in early flower and turn it off in late. This more mimics nature in that as fall comes (flowering season) the light intensity deminishes rather than get brighter.

That does make sense. They just really started fattening up. Probably drop them back to 600. Thanks.