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I'm not sure I understand the question. German fire intensity has nothing to do with preservation moves, the only requirement is that you get towards a safe hexside.
You should also never have any infantry units eliminated due to rising tide. That's what the preservation moves are there to prevent.
That doesn't imply that infantry units are allowed to make a preservation move onto the mid-tide hexes. Right? In doing so, they would receive increased fire from the Germans.
If you leave infantry units lingering at the base of the Eastern cliff instead of having them climb or move, those units would be in danger from the high tide and not have a valid preservation move available. Hopefully the times when you can't afford to spend an action on a cliff climb move are few and far between though.You are right John, I generalized without considering any exceptions.