Stanley's telling of the fall of faq rammed home a very important fact about city defense.
Casters and tower defense spells are the primary threats to be considered when invading a city's airspace. Stanley doesn't mention archers at all when he describes losing those 10 dwagons. This fits in with a number of other incidents. Book 1 told us that casters get a bonus when casting from the tower. We see Wanda and Maggie dropping multiple flyers, including knight class archons, with spells/ tower defenses. Ceaser describes the effects of tower defenses against airborne attacks when we found out Transylvito is popping a heir. When Parson gives Wanda the numbers for burning the Jetstone garrison, he tells her that the biggest factor is what type of caster Vanna is.
Since casters are such a big threat to an air raid, tactics for raiding cities with flying units need to be centralized on what an enemy is known to have in terms of magical defenses. Ceaser's tactic of eating any penelty incurred by having a flying unit not fly is one method, but there are probably better ways to deal with the problem. (ie: feints designed to split up types of defenders based on move is one tactic if the enemy has multiple targets for you to attack. Can also be used to have an enemy caster prepare defenses in the wrong place.) Feints only work in certain circumstances however. Sometimes you will have to send in the air forces into a caster defended city.
Tactics for when you have havbe at least on caster are easy to come by depending on the caster. Foolamancy seems to be a good option. Turnamancy is better. Thinkamancy may provide the funnest option if you can pull it off. (DDOS Archon thinkgram attack, interrupt casting of any spell.)
Tactics without a caster for the attacking side are trickier since the rules state that the tower, as part of the garrison, cannot be attacked without control of airspace or another zone. (This rule is stated in book 1, but we never find out the strictness of it.) This means that while an air force is seizing airspace, the tower casters will be free to spend all the resources at their disposal against you. Sending in almost literal cannon fodder to absorb damage isn't entirely out of the question. But depending on the situation, the enemy may be able to hold back defenses to use against a main force despite the fodder.
Another, possibility presents itself to an attacker depending on how strict the can attack garrison without outer zone control rule is. If the physics are anything like off turn archery into the tower, then you can try to block a caster's line of sight with a crap/ ration/ cannon fodder barrier around the tower.