As I said, blasts inside the water increase the blast damage, but that falls off much faster with distance as the thick medium dissipates the energy - it really helps if you attach the bomb to the hull underwater but in AH you can call this a direct hit. If you insist on more accurate modeling then the underwater blast radius should be decreased and damage within that radius increased. I did not go that far with my wish.
Yes, a very near miss will do damage and this is why the blast radius should not be decreased to zero. It is not accurate that a near miss is better than a direct hit. A direct hit may not breach the hull, but it wrecks total havoc on the ship, effectively disabling it for an extended period. Coastal command sank ships or effectively disabled them till they could be repaired at a dock with just 20mm cannon strafing. The fires and explosions did the rest.
IIt wouldn't make a difference The few planes carrying AP/SAP would still be massively outperformed in that mission profile by bombers or heavy fighters. Both in flight performance as well as punch carried.
Not a big difference, but it still gives them more effective loadout without the disadvantage of lower blast radius. So a P47 will bring more total lbs, but now he will need to hit as accurately as the SBD and not settle for a water splash.
In any case, that was not the main goal of the wish.
Drop the amount needed to sink a CV to 6000, and maybe.
Fine tuning that can be done later. Irrelevant to the wish.