I was reading how container plants can get hit pretty hard by frost because they are above ground and pretty much right where the coldest air sits. They can freeze faster than if they were in ground. Have you thought about burying the pots in a hole and filling them in loosely? That way they would have a some some heat from the earth. I haven't tried it yet but it's worth looking into. I'd mulch them heavily around the trunk with leaves.
Right now I have the luxury of "not too many plants" and "all can be carried". But yes when a pot is becoming cumbersome to move, this is an intermediate workaround. Even covering the whole plant for a few days, probably is better than allowing it to go through once-in-twenty-years temperature extremes.
You're right that cold air pools in low areas. My yard has a moderate slope. When I have checked the temperature in a far corner, it will be about 5 degrees colder than my reference point thermometer, which I keep on a railing near the kitchen door. I know that 20 feet or so from the house will be 2 degrees, so that other 3 must be from the descending cold air.
Interestingly, the lowest point on my property is a drainage hole surrounded by elderberry bushes. By this time of year, the elderberry is completely barren of leaves. But the branches still provide protection from radiational cooling. The ground in between them all, usually does not frost.