Hi
If you do hedge accounting and run the effectiveness test the system can post the effective part to OCI and the ineffective part to P/L. If you have an hedge item of 100 USD and hedge of 100 USD the trade is 100% effective. If you have a hedge item of 100 USD but you only hedged 90 USD 10 USD are ineffective and will therefore post to P/L.
Please check help.sap.com for hedge accounting.
Kind regards
Juerg Heiz