the sealing of the hole is also affected by tire pressure and the width of the tire . too high of a tire pressure will just make the sealant burst through the hole. In my experience anything larger than about 3mm is going to leak and sometimes event one plug is not enough. You need to double up the plugs.
I would never add water to replenish. I mean cmon. Just pour more sealant in if You are low on sealant and let the sealant work as designed.