How to navigate a CI buffer

I'm on FSCM 9.2.28 and Ptools 8.57.21.

I'm trying to set a value in the Component Interface buffer from the Component buffer. Then retrieve that value from within the CI.

Here is a snippet of my code that appears to work - but the value is not there later at time of Save.

     &oPvProcureReqV3Ci.M_PR_AP_FILEAT3.OPRID = &rsIMG.GetRow(&I).M_PR_AP_FILEAT3.OPRID.Value;

     &oPvProcureReqV3Ci.M_PR_AP_FILEAT3.ATTACHUSERFILE = &rsIMG.GetRow(&I).M_PR_AP_FILEAT3.ATTACHUSERFILE.Value;

     &oPvProcureReqV3Ci.M_PR_AP_FILEAT3.ATTACHSYSFILENAME = &rsIMG.GetRow(&I).M_PR_AP_FILEAT3.ATTACHSYSFILENAME.Value;

The "&oPvProcureReqV3Ci" is an apiObject from CI PV_PROCURE_REQ_V3_CI.. "M_PR_AP_FILEAT3" is defined in the CI and it should be a Collection - like a table or rowset with multiple rows possible. But I can't get that part to work either.