In my opinion it's not a function of how many AD's you have, but 1) what morale bar do you set for resting air groups; 2) how often you fly air groups; 3) the specifics of your AD's, such as altitudes, flight paths, escort levels, and interceptors likely to be encountered; and 4) using Fighter Command and Malta Air Force to do CAP missions. 5) It also helps to rest air groups if they won't be flying during an air phase and/or during the enemy air turn.
In fact, in my opinion the more AD's the better, which is why I now exclusively play the 1943-45 AAHQ Scenario - with Additional Air HQ's.
1) At the beginning of every turn I use the Commander's Report screen to first set all air groups to "0" Day/Night. Then I filter to air groups with Morale of 54 or less, and set them all to Rest. Then I filter to just Transports and set them all to rest. I then assign air groups to AD's. If I have FB and medium LB air groups with low morale, I remove them from GA AD's and assign them to the Ground Support AD, and likewise remove any FB's and LB's with good morale from GS AD's and assign them to GA AD's.
5) Skipping ahead: After the friendly air phase I use the CR to filter air groups by Air Directive type. I activate the groups assigned to GS to Day/Night and I rest the GA, SB, and Rec air groups. Because I fly both NI and AS AD's in both friendly and enemy turns, and rest half of the air groups assigned to each AD of those types in the friendly turn, and the other half in the enemy turn. If you're going to use your TR's for any reason, don't forget to reactivate them to Day/Night. Also at the end of every friendly turn in the CR I Add Pilots/Trained Only, to restock my air groups for the enemy turn and then the next turn.
2) I NEVER fly GA or SB AD's more than three days a week unless it's an emergency. If you do this, most of your GA and SB groups will have 55+ morale every turn. If you fly more than that, it takes multiple turns to recover. I fly Rec four days a week (1/2/3/6), and I fly AS and NI every day, but I only Request AC for 1/2 of the available aircraft, so effectively I'm only flying each FB-F, PA, and TB plane 3 1/2 days a week.
3) Use the four way points per AD to avoid flak by at least one hex and ideally two hexes. Fly at least 21K' unless you know for sure that the target is completed undefended from flak.
Don't fly to Ruhr or beyond without escorts. In fact, I usually over-assign FB-F's per LB for a SB AD. For example, I may assign 100 B-17G's to bomb Kiel, and assign 200 P-38G's to escort them. In that case fly at 23K+ to take advantage of the Allied altitude advantage. My air campaign strategy is to attrit the LW day interceptors as early in the scenario as possible, so trading American FB-F's for equal or more German FB-F's is fine with me, assuming I also damage my targets.
Fly NI's at 16K', because the Sunderland has a max altitude of 16K, but if you get rid of the Sunderlands not only can you set a higher altitude, but also the air group size changes from 9 to 12.
4) Set up Fighter Command FB-F's in 4-5 large air bases from Boxted in the East around the South to Exeter in the West. Put your best FC air groups at Boxted and convert as many as possible to Spitfire VIII's, which have the longest range. Set up a size 4 AS AD at 24K+ altitude for them as far out over the path to the Ruhr and Hannover as possible. This provides CAP for your daytime SB missions.
The other FC AD's should be size 4 and overlap in size and location COMPLETELY with the Coastal Command NI AD's. Some people transfer the FC FB-F's to Coastal Command, and while I generally don't feel constrained by history as much as some other people choose to be, I find that my system works fine to provide escort. I fly those FC AS AD's at 21K', so they're within the 5K' band to support the PA's and TB's.
You can set up a Malta AF size 4 AS AD over Messina at the beginning of the 1943 campaign and do something similar.
If you want more detail or an explanation on any of the above, let me know.