The input scaling simply defines what engineering unit (EU) should represent 0mA and what EU should represent 20mA. If the signal goes beyond 20mA, then your value will continue above the 20000 you defined for 20mA. Likewise if you defined 4mA as 0 (EU) then if your signal dropped below 4mA then your EU would be a negative value.
The module you are using is capable of detecting a signal from 0 - 20.58mA.
OG