SD7.5 Priority Auto Calc on Incident Response Form

For ServiceDesk 7.5, does anyone know how to get the Priority "Auto Calculate" on the Incident Response form to work for custom priorities?  Thats the form that opens when you click on the "Work Incident" task for an existing incident.

I see that http://www.symantec.com/docs/HOWTO81841 mentions changing the Technician Feeder form but that only affects the Advanced Incident creation form.