I think 2.2 gal is plenty big enough.
Because having roots able to access only a small amount of water seems to be working well, I'm going to also do a small DWC-AutoPot semi-comparison grow.
Instead of the two 2.2 gallon autopots I'll be giving 2 dwc plants 2.5 gallons each in a half-filled 10 gallon reservoir with a float valve to simulate part of what AquaValve does. The top tan bucket is the storage reservoir, and the empty bottom tan bucket is present only to lift the top bucket.
One worry is that roots will incapacitate the float valve inside the plant reservoir, but I've got access to the float valve to free it of roots if needed.
It might also be difficult to keep the external storage reservoir with the same pH and ppm as the plant reservoir.
But I'm hoping that I can "lead" the plant reservoir by anticipating how it will change storage reservoir conditions, if it does.
In other words, I'm trying a hydro version that I hope will be simpler and at least as effective as AutoPots.
Disregard the large black sump pump, the dirt plant, and the red-topped sprouter.