Re: STO – Availability Check (at MRP area level)

Please read OSS note 2122786, you can find detailed description how ATP check works with MRP areas (in customizing you can influence the behaviour with indicator T441V-OLGPR).

SAP help also provides basic information about it ( ATP Check with MRP Areas):

http://help.sap.com/erp2005_ehp_07/helpdata/en/cb/a9ce5314894208e10000000a174cb4/content.htm?frameset=/en/80/2eb853dcfcb44ce10000000a174cb4/frameset.htm&current_toc=/en/80/2eb853dcfcb44ce10000000a174cb4/plain.htm&node_id=180

You could also check OSS note 154682  which describes a special case (when you enter the batch manually - based on your description it is not the case but you may use this scenario as well).