2'' is too close for a light to be near a plant. The light will be too focused on a small area, so I would keep it at 6". It seems that whatever your soil is , your plants don't like it', so you might be looking at a shock situation, which will take about a week to straighten out. 4 gallon pots are a bit much for a pot plant, but there is no harm using one (1 gal per month of growth) It definitely isn't overwatering, because if it was, your plant would be dead by now. I personally would carefully repot again, leaving the MG soil out of the mix. Use the best soil you can find, mix with a decent amount of perlite, and feed lightly (650-700 ppm for a 4 week plant is fine) with a grow solution that favors N. I would water every 3rd day, with a light feeding once a week. Oh, and by the way, at 4 weeks in would be advisable to use some Calmag, which has extra N in it, because around that time the plants could use a boost. Good luck