The issue is that the "excess" lines and the Schedule A are mutually exclusive.  If it's excess then, by definition it's not on Schedule A.  If it's allowed on Schedule A, it's not excess.

Since you're prorating both by square footage and by number of days you may want to do the math outside of the software and manually enter the numbers on the appropriate forms.

Mathematically, the distinction between lines 10&11 and lines 16&17 is only relevant if you end up with a Sch C loss after the home office deduction.

The Force Standard / Force Itemized option is on the Fed Info Sheet (scroll way down).

Rick