Release strategy for PO

Hi Friends

I have an issue in PO release strategy. I have created characters for

1. Material Group

2. Plant

3. Purchasing Organisation

4. Purchasing Group

5. Net Order value

The condition is like this: One user A uses Purchasing group B to buy certain materials having material group C. If the value of the material goes above RM 500, the release strategy should be activated. I have created characteristics for all above mentioned points. I have assigned these characteristics to a class. In all the characteristics, I have assigned the table CEKKO and respective fields for plant/material group/purchasing group/purchasing Org/Net order value. I have created release group, release code, release strategy. In release simulation also the status is "Release Possible/Release Effected". But when I create a PO and assign that Purchasing group/Purchasing Org/Material group and the value of the PO more than RM 500, the release strategy is not activated for PO, where as same type of characteristics created for PR (Using CEBAN) is working perfectly fine.

Please suggest how to activate the release strategy.