Update for contract release value

Hi Experts,

I am using a value contract for service. I have created contract release PO with reference to the contract  . The release value in the contract is updated by the PO order value. Service entry sheet is performed and final entry indicator is set . However the amount of the SES is less than net PO amount.

Contract Target value  $ 10000.

Contract Release $ 1000

SES confirmed $ 900  ( with final indicator)

According to this scenario. the Contract remaining amount is 10000-1000  = 9000 so the next PO can be created upto the amount of $ 9000. 

If we delete the unused item or reduce the qty in PO we can reduce the Contract release amount accordingly in Contract. I have tried deleting the PO item which has the service items after GR and IV still the release amount doesn't decrease in contract.

Is there a way to reduce the contract release amount in contract after closing the PO without changing the qty and deleting the service items ?

Cheers

Paonam