The range that you can use has a minimum value of 5; the maximum value is based on the following formula:

MIN(32767,MAX(4096,3*initial value))

The initial value is the MAXPROCSYS value that was specified during BPXPRMxx initialization. You cannot use a value less than 5. If you want to use a value greater than the current maximum (as calculated by the formula) but lower than the initial maximum (32767), you will have to change the value in BPXPRMxx and reIPL.