Thanks for to all, for all the comments on weak stock and wintering!

One thing that cropped up is that individuals mention about placing
colonies on top of others - for heat support etc.

Omitted is what is the piled box configuration!

So how are the piled colonies separated from each other?

With inner covers only, queen excludes - or any other permutation?

For good heat transfer from bottom unit to supported top unit: I presume
that the bottom one has its lid removed, inner cover only in place, with
the upper unit having its floor in place.

I should put my mind to an intermediate screen of some sort allowing
better heat transfer to take place. Then investigate.

The above comment made realising that cold does not kill bees unless
allied with lack of food, and that higher winter temps. result in faster
rates of reserve consumption.

And I do not wish to have a constant supply of weak colonies to test!

Conclusion:

Successful wintering here abouts comes down to adequate food, well
prepared with a good number of healthy winter bees.

Thanks again,
Peter

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