Off Map Artillery
 

Doesn't it represent artillery that's near the battlefield, not near enough to be located on the map, but near enough for indirect fire? As an option, I think you should be able to turn it on and off for either player before a random battle starts. For example: for use on small islands when a side has naval supremacy, plus there might be other logical uses for it too (mountainous terrain, or maybe it's just not availble, etc.). It's not fair to the other player if it has to be implemented as a house rule.

Re: Off Map Artillery
 

Not sure I understand I assume you are talking about the island getting off map artillery as the attacker will get naval.
The odd situation like this airdrops & mountain or jungle troops out of range are best covered by house rules or scenario design.
Mountain or jungle would most likely be restricted to mortars pack howitzers & maybe RCL, of course vehicles would also be restricted as in most likely none existent or pack horses if you want to class them as vehicles, hence house rules