great thread so I thought I would contribute.
I stick a single probe moisture meter right into a hole at the bottom, about a third of diameter of the pot in, don't want to touch the tap root.
then I water from the middle really slowly, but not with a watering can, I use a gravity drip bag feeder.
I only use one pipe from the bottom of it tho, not a line, and put that in the middle of the pot.
fill it up with what you think, they can hold 6l max each bag,, and walk away,.. come back if probe reads wet, I check other holes to see if reading is the same.
if not, leave the probe where it is and carry on slowly drip feeding her.
They love the slow drip drip drip dripping, bit like I rain I spose, running down the centre stalk.
And some one said that if you water from just the middle, concave soil or not, then the water may not reach the sides?
yeah it does if you water slowly enough, or it will just bore a hole through and out the bottom or gush out of the sides,,,nice and slow is the key with airpots and,, from the middle., Superb advice that is Tang, nice one bro,. I myself learnt that from yourself many many grow cycles ago,. Much kudos bro.