Z: I don't think that's the reason. Since the new engine, I've played in all three divisions, and I don't see that as the issue. I can't tell you exactly what the issue is, but I don't think that's the reason for the apparent discrepancy.
I have had multiple guys whose ath/reb were the best on the court in nearly ever matchup end up averaging mediocre reb totals. Take Randall Alexander for instance. Playing man, he should be pretty dominant on the boards, even at D2. But he's not. And I see this all the time.
I don't want this to necessarily turn into a rebounding thread. But I do think that rebounding logic problems are helping the press, especially at D3 where, as you stated, it should be easier to have dominant rebounders if that's what you're recruiting for; only I (again, not this year) generally do have big ath/reb guys, and I'm not seeing dominant rebound totals.