Are you using COPQ to measure effectiveness of your organization's QMS process or your process (i.e. Quality as a quality manager) or your KPI as an individual? I don't think COPQ is right measure for QMS process. For Quality process, it is.
For determining effectiveness of process, determine what outputs are required out of the process. Eg. Output required out of QMS process can be Effective quality management system- which can be measured through "Number of repeat Internal audit NCs", "Number of Major NCs during external audit", etc.
Definition of Effectiveness as per ISO9000:2015 is extent to which planned activities are realized and planned results are achieved.
Efficiency on the other hand is "utilization of inputs/resources" or "to the extent to which time, effort and cost are well utilized". Definition of Efficiency as per ISO9000:2015 is "Relationship between the result achieved and the resources used". Time taken for closure of NCs, Planned Vs Actual completion of internal audits, etc. can be efficiency measures of QMS process.