The Optional Parameters field is only 58 characters long. This makes it difficult to parameterize things. For example, if you want to pass a dataset name, you could use up to 44 characters. Add a one or two more parameters are you are out of space. There is plenty of room on the screen to accommodate additional lines for this field.
Here's an example from one of our user class resource definitions:
ProcessName Optional Parameters
WAITCHK ENV=DEV JOBNAME=FTP2SERV RESNAME=FTPS WAITMINS=15
I would like to change the ENV parameter to a DSN parameter and specify a dataset name, but it won't fit.