The game engine penalizes non-attack bombers in low level (1000 feet or less) attacks by defaulting them to their reduced (extended range) bomb load.
Not 100% sure, but I think this was changed somewhere along the line, and is no longer the case.
The controversy over this really relates to how the code works when it comes to bomb loads and hits. Now don't get me wrong, I've no magic access to the code, but this is as I understand how it works.
So a four engine bomber carries a large number of bombs (relative to other A/C) and when it bombs its 'hit rate' is generated with this as a factor. So they tend to get more hits than other bombers making them a bit more effective than they might have been otherwise. Now this is necessary when it comes to say city bombing as otherwise you may get no result, but against shipping it may not be the case. So the Dev's had to code as best they could to have things work in the overall picture. Could it have been done otherwise, sure if you're the DoD and your budget is basically unlimited.
So players balked at the practice and HR'd it many times to 4E bomber must stay above 10k when bombing shipping. That doesn't include 4E naval bombers in cases I've seen. TBH, depending on the type of ship 2E bombers do a pretty good number on shipping too and the Allies have plenty of these so... Its again up to the players and how they wish to play.
Of course the above is JMHO. YMMV. Ciao
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