Problem in service contract determination using spare part items

Hi experts

I created a service contract with spare parts in product list, and discont for those spare parts in price agreement. The spare parts item category group is SRVM.

If I then create a serice order and add the spare part as the item of the transaction, depends on item category I put in for the spare part, contract determination may or may not happen. If I put SRVP ( service product) as item category then the contract determin will happen. But SRVP is not allowed for the spare part product. If I use SRVM as item category, then the contract determination will not happen at all.

The questions are

Can contract determination be triggered by item category SRVM? If yes, what do I have to do to make it happen? If no, what item category can I use for spare parts to trigger the contract determination?

Your help is highly appreciated.

Ming