You can search for similar threads on the top right hand corner search function. @m1tanker632 To be honest I am not sure but a while ago, some people were complaining in the forum about enemy planes flying near/over the AA without any damage but some say they do damage so I am confused too.

cruisers and destroyers can provide AA defense if close enough to the LZ.
same with AAA that are already ashore.
There might be some differences in the amount of damage done to the planes,
depending on whether they are attacking or patrolling.

The close combat radius of all attacks is 5 km, so if a direct attack is done on a disembarking unit at the shoreline, any AA or ship within that 5 km will return fire, damaging the plane.

If there is excessive space between the disembarking unit and their support units the enemy might be able to patrol precisely enough that the fragile disembarking units are within the patrol circle and the supporting units are not.

Naturally there are times that your ability to move naval units closer to shore is disrupted by the automatic snap distance. On desktop this can be circumvented by holding Ctrl key when moving a unit.

Also, most of the time people will be patrolling, and if a cruiser/destroyer is within the patrol circle, it will take damage but your convoy will probably be taking a lot of damage from the planes anyways. Thus, you probably shouldn't land somewhere being patrolled or attacked by planes (especially naval bombers)

Does this mean if there are two separate stacks less than 5 km apart, and you target one of them with ground troops, then your unit will engage both stacks in 'melee' since the other stack is also within the CQB radius ?

try as you might, there is no scale on any bystro map
or any other means of measuring what 5 km is.
good luck trying to guess which enemy or friendly unit is within the 'magic' 5km cookie cutter range.

This would be a good future mod to all maps! ...

Yes, The same applies to this as where you asked this elsewhere earlier today Marechal.