CAS and ADA can be frustrating at first, but after playing many different battles I've found that a lot of the time it all just comes down to luck.
Sometimes your ADA will be effective and sometimes it won't. Sometimes the enemy CAS will wreak havoc on your vehicles and sometimes it'll be lucky to get a single hit.
Enemy ADA plays under the same rules, so sometimes it'll manage to take out your CAS on the first try and other times it'll be entirely ineffective and your CAS will be free to wreak havoc on the enemy.
Hiding under tree cover hasn't seemed to help much in my experience, but I guess there's a small chance the ordance will impact a tree instead of its target. If anything, it seems like Trophy APS equipped vehicles moving across open ground have had a better chance surviving CAS in my games.