Help: billing settlement days for monthly billing on the last 3 days

Dear experts,

We configured standard monthly billing for contracts.

But we noticed following behaviour by sap:

If the contract start date is in the last 3 days of the month, the next settlement date is counted backward in next month. E.g.

Contract starts on 2013.05.29

Billing cycles are:

2013.05.29 - 2013.06.27

2013.05.28 - 2013.07.28

What we are expecting is:

2013.05.29 - 2013.06.28

2013.05.29 - 2013.07.28

Is there any configuration can influence this behaviour? And how to handle Feb (28 days / 29 days)?

Thank you!