I think when you get to one gallon pot size with plants these size you need to feed based on the plant size and not the pot size.
My organic dry ammendment grows greatly improved with 2 things thanks to
@Shaded_One, 1st was just adding more fertilizer more frequently, 2nd was calcium and magnesium supplement via gypsum and epsom.
You got them the magnesium that will help, get them more 2-8-4 and rock dust/gypsum, and then see if you can boost the beneficial microbes to kick things into gear. Do that every 2 to 3 weeks and they will stay happier longer. Just get better each grow and never give up