I think you're trying to get too scientific without having the basics down first, watering and environment is more than half the battle. Next grow, have the same size pots with the same age plants and preferably the same strain to really get a handle on your watering practices. I have plants at 3 different ages and it's a pain in the ass... I literally write my notes on a calendar or my stoner ass will overwater someone... a cheap moisture meter for insurance isn't a bad idea either. Right now I'm I'm in .75 gallon pots, organic soil, extra air holes, decent environment (temp 75-80, RH 60-65) and I go 5 or 6 days between waterings, my oldest are only a month old, younger are all around 2-3 weeks, obviously bigger plants in flower drink more.