what foams work better with the axial weight ring 1.9

[TacoCrawler]

I think it is more probable..

That you trapped denser air molecules inside the tire by freezing...
and when that tire warms up to the exterior ambient temps...
expansion occurs and causes the tire's trapped air molecules to expand slightly.

Did you measure the foam inserts (stand alone)
before and after their freezing process ?

or simply the assembled tire diameter before freezing
and after ambient warming ?

Whatever works for you as it's your game
But the science of your methods leaves me befuddled.

Tho' the end results may net what you desire...
how that occurs is not due to the foam inserts contracting or expanding.
And if I were a gambling man, would wager a bet on that.