Overlapping absences and plan use

We are trying to set-up the following for our absence administration:

• Absence type 1 - accrual - linked to absence plan A
• Absence type 2 - accrual - linked to absence plan B

Both plans are set up to allow for concurrent entries.

What we are looking for is to setup the plans in a way that when there are overlapping absences for any day that the absence is only deducted from plan A and not from plan B. Currently for these overlapping periods both plans are credited.

Any pointers on how to best configure this?