willistoned this what I would do, if she was mine, after hearing you say that the lower leaves look better, I would raise my light 4-5inches, but again, I'm no plant doctor,
Your lower leafs, turning yellow is normal, like you said.
I'll tell you something else, flushing plants grown in soil, is ruff on plants, especially when they don't need flushing,
Flushing growing in coco, ain't nearly as bad as flushing in soil, imo.
Have you ever thought about making your own soil, it's easy to do, and almost impossible to mess, them up, in no time you want even have to ph, your water.
And that's all you need is water, but I use molasses too.
I done got so old, that's all i use now, is living soil, it's super easy, plus it grows some powerful an great smelling MJ, too.
Good Luck with whatever you do, your plant will be ready, to harvest, in no time.