I agree - adjusting the 'sensitivity' is pretty much a plane-specific thing, and it also means understanding what the flight dynamics do.
I would approach the .air file with caution for a couple of reasons: a) it is pretty cryptic, even with advanced editors like AirED (available here), so often you can't be sure what it is that you're changing, b) many of the important settings are fine-tuned in the aircraft.cfg file. In fact, you can leave the .air file pretty rough on design, and fine tune on the .cfg. There are a couple of settings that are found in the .air file though, that have no .cfg file equivalent: like Mmo (max. Mach speed), airframe type, drag and braking strength.
So, it may be better to tune in the .cfg, unless there really is something that needs changing in the .air file. If your 737 is flying like a Cessna, then you might look at the airframe type in the primary aerodynamics section of the .air file (line 1101) and compare it wath that of the default Cessna or 737. You might be able to tell whether it's a Cessna or 737 .air file that's been used as a template - or indeed the .cfg file too!
The plane's reaction will be determined by the weights etc. that can be adjusted in the geometry section of the .cfg, and then fine tuned using the flight tuning section mentioned above, if you find that the plane is porpoising uncontrollably, for example.
Good luck!
