Hello, Folks,
The following dissertation is my understanding of the effects of bombing the City Strategic targets, which are all clustered together, and include the large City, which is identified with the "C" icon and the other outlaying icons that represent the Fuel Refinery, Troop Training, Ordnance, Anti-Aircraft, and Radar factories and how they relate to the Airfields, Ports, and Vehicle Bases.
The key is the City because it supplies the other five (5) outlaying targets: Fuel, Ordnance, Troops, AA, and Radar. When you bomb the City below 50%, it affects the City's ability to supply the other five targets. The key here is the further below 50% you can bomb the City, the longer it takes for it to regenerate its ability to supply the outlaying targets.
The firsttime you reduce the City below 50%, it will retreat from its forward position on the Map, and move to a position farther away from the "Front Lines". When the City retreats to the rear, it will regenerate visually (you will see everything is still up) but, tactically it is at, or below 50%.
Then, bomb the City to keep it below 50% again (remember...the retreat was at 50%; further bombing takes it further below 50%), and send your Bombers to reduce each of the other five strategic targets below 50%: the further below 50%, the the Strat targets are, the longer it takes for the target to resupply the Airfields, Ports, and Vehicle Bases. Again, the key is the further below 50% you can bomb each Strategic Target, the longer it takes for it to supply the outlaying targets at the Airfields, Ports, and Vehicle Bases.
Next, bomb the individual strategic targets at the Airfields, Ports, and Vehicle Bases; it is at this point where you will begin to see longer rebuild times for the individual Strategic Targets on the various fields.
Good Luck, and Happy Bombing!