You experienced the "squat effect" which actually increases a vessel's draft (your words were sucks us down) when operating in shallow water. Cutting your speed in half reduces the squat effect by a factor of 4.
They just have to be below surface. They are flighty angled away from barge. Not angled that it affects accuracy, just away from barge a bit. Pretty simple deal
See them about every time the river falls kinda fast and tugs don’t get fleets pulled. Kinda regular type deal for minor groundings with fleet barges, as they are usually leaned against bank.