Lets plug your numbers into this and tell me what you get.
CFM = volts x amps x 3.412 / 1.08 x temperature rise
= 237 x 20 x3.412 / 1.08x 19
=16177 / 20.5
788 CFM
You need 400 CFM per ton so Id say your as good as it gets air flow wise. 12 CFM isn't going to mean jack s*it in over all performance. You are more than welcome to look it up on a fan performance curve.
Air flow isn't causing your HP to be noisey while switching into and being in defrost.
Moving along..
3.412 BTUH = 1 watt.
To find BTUH using the temp rise across a electric heat element the formula is the Sensible Heat Equation.
BTUH = E x I x 3.412
Now that you know the BTUH you can find CFM by using the formula at top
To find BTUH in heat mode;
BTUH = CFM x TD (db) x 1.08
To find BTUH in cooling mode;
BTUH = CFM x HD x 4.5
HD = total heat difference ie. Enthalpy DT measured in wet bulb across the HX. You'll need a total heat chart to get those numbers unless you post accurate wet bulb numbers in cooling I cant help.
4.5 is a constant, once again at sea level which changes with altitude. A mute point in your case.
Now throw those s*it equations in the trash and get to work.
Otherwise I will enjoy my morning bowl of Coco Puffs for breckfy and thank God you helped to make it possible. :)
Hope this helps.