> Recommended dose is 2 strips per brood chamber.  So for most of my
> hives, I'd need 4 (or perhaps 3 for weaker) per hive.

We treat bees, not boxes.  I assume that whoever wrote the label assumed
that the aforementioned boxes were full of brood.  In fact, I have
seldom seen more than ten frames of brood.

Killing the phoretic mites is a slam-dunk.  The mites hidden in brood 
are the difficult ones to get.

If the varroa density in the area where the the brood is about to be
sealed is 5X to 10X that on the bees that are even a few frames away,
why place strips anywhere else?

I say, "if".  The only time I checked, that was the case.

AFAIK, Alberta beekeepers use two strips, with a few exceptions, and
have good efficacy, but perhaps due to the season, the bees are less
spread out and the brood is in a smaller volume.

Of course you should follow the label literally to the letter.  It's the
law.

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