you are a field technician...copeland and every other compressor manufacturer will tell you that you need 20F because you have crap equipment, spend 5 minutes on troubleshooting and you dick with the txv everytime you have a chance...well, maybe not you, but you get the picture.
if you are a manufacturer...then compressor manufacturers will allow you less because you test everything many times over with NIST equipment and then you write it down in the IOM that you need to have 12F suction superheat (or whatever).
that's the difference.
"I got both hands on the wheel
And my big foot on the gas"....Chickenfoot