ORIGINAL: golden delicious
Right. So on passive defence they're offering around 20-30% of their maximum strength while at sea. That's not bad. However if they were able to bombard directly you'd still be looking at around half of maximum strength on the first round (which is 10% of the first 3.5 days, or about 8 hours). Moreover if they were directly bombarding every round, after the first few their strength is no longer declining.
Look back at the start of this AAR and note that no artillery units are directly supporting in round one. That's because they aren't in range to do so without moving first. Furthermore, there is only space for one unit at Utah and one unit at Gold/Juno to even make that move (and those were, historically, the two easiest beaches - Omaha has no such support on round one). It will be well into the turn before much of the artillery can be brought into action.
You don't need to object. I'm explaining how this (the artillery becoming unavailable if they directly bombard once) is a feature, not a bug.
Well, only if the Allied player is dumb enough to do what I did. A little patience gives the benefit of moving the two units onto one of the sea-road hexes, where that won't be a problem.