Superheat requirements vary with systems a bit. Many factors can contribute to actual super heat readings vs. system design requirements including installation quality,compressor valve condition, condition of the machine evaporator and condenser coils (Air flow issues), a split system design with long improperly insulated tubing set. The possibilities to complicate it are endless. A few things to know up front when checking superheat are:
What refrigerant is handled by the system?
TXV, cap tube or flow orifice design?
Is the machine running under full load and stabilized?
Anyway here is a link that may help or confuse the hell out of you lol.
Best of luck!