JES always passes a form number, such as STD, so there is no way to override that value as a DEFAULT.
Forcing a value does not work because that would override a form that was specified as something else in the JCL.
It is also not possible to use the default form number assignment on the DFORM parameter on the DESTID statement when the XFER SAPI interface is used. This is because the primary CA Spool system will still pass the form number defined in the JES parameter library.
Example: DESTID DFORM=1234 - This statement is ignored.
XFEROPT=23 can be used to suppress the JES default form number which is defined in the JES parameter library that is passed to the XFER SAPI interface.
When the FORM name passed from JES to the XFER SAPI interface is equal to the DEFFORM in the CA Spool parameter file, XFEROPT=23 will cause CA Spool to bypass the use of that form name on the open request for the file. This allows either a DESTID or the NODE FORM parameter to provide the default form name to be used. If no DESTID or NODE FORM is defined, the DEFFORM value will then be used.