Beginning of Period Lease Payments

Hello,

Where do I indicate whether the lease payments should be made at the beginning of the payment period or at the end of the payment period?

I do not see any button to click or box to check. I click opening posting it automatically posts. Perhaps the indicater is in the setting for the automatic posting. Where can I find that? Transaction AS03

We are useing ERP 6.0. Enhancement Pk 7, Support Pk Stack 2, NetWeaver Release 7.40