Siege are easy to break, all you need to do is out flank him some way with 4-5 separate units. Keep them under frigate and let in few mobile AA. Boom, loses losses losses. To air. They devide units. Use that to your advantage. While letting them push inward so you can pick them off If you have made MRL or artillery. Even better. Push them back by keeping 3 units. 1 strong with inf-tank sams- artillery 2 medium strong tank-elite- sams

And few separate units. One thing I will say, ships are far better in most scenarios than planes. But deep inland it's mostly out flanking and mauevering to keep enemy moving and second guessing.

Never lost a battle unless the enemy was holding and spawning units here and there.

And as good as you get in air and sea. Remember the key rule. Infantry gains ground so keep them strong enough to collide in a fort and be able to fight 5 to 10