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Adam,

You wrote <... how can air flowing around an injector
affect its fuel flow? Is the air leaking into the injector at the
fitting??>

Considering the dearth of replies, you must not be alone.

Close inspection of any injector body will reveal a screen to protect
particles from entering the injector along with the small amount of air used
to help atomize the fuel.  Also note that injector installation usually
requires that the letter stamped on a face of the hex area is to point up (or
down, I don't remember which) so that the air hole is facing up to lessen
fuel leaking out after the engine is stopped (a small amount in any event).  
Air entering the upper engine cooling plenum does so at a speed in excess of
200 mph (remember that a high power leaf blower only gets the air up to 150
mph (a good one, that is).

If different injector atomizer air holes are subject to different air flows
and pressures, the atomization of the fuel can also be different resulting in
uneven fuel/air ratios.  Note that the #2 injector is the first thing to see
incoming air.  It may be that even the position of the air hole is important.
 

Another example is that turbo/super-charged engines use special shrouded
injectors supplied with deck pressure air to reflect the artificially raised
manifold pressure (as opposed to ambient pressure) to supply atomized fuel at
a known and repeatable rate.

I hope this helps,

Scott Krueger
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