Campaign tactics - zone breakthroughs and deployments

[broadsword]

Uh oh -- I just noticed a nuance in this breakthrough rule:

" ...then non-activated enemy units deployed to the area ***may*** set up at that time."

So it's optional, and it means the British player can't **force** the Germans to commit and deploy onto the new zone if the Germans would rather delay their deployment onto the new map sector until later.

Of course, by waiting, the German player in my example would be giving up territory to any British advance in the new sector.
And if the German player does wait to deploy in the "breakthrough" sector (Odon Valley-East), when exactly does he do it? Any time during a British pulse that he decides to suddenly appear on the map? Or only on his own pulse? Does it matter?