i forwarded this question to an engineer friend (the kind of engineer that actually builds things), here was his thoughts:

"wow, this is a tough one.

Shrinkage in materials that are freezing (in the general term) is common. With metals, we call it caving. You see it in castings all the time.

I think this is similar to the shrinkage that we see in waxes for casting.

He says that the lower temperature rendering results in less shrinkage. He also says that the lower temperature results in better aroma, texture and color properties. Without knowing the chemical composition of bees' wax, my guess is that the wax is losing water and aromatics to the higher heat. Those materials may cause a 'fluffing up' of the base material like water in a sponge.

Careful density measurement of the two styles of rendering end products would yield some good data.

Jim"

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