Hi Rf planner,
The thing is with interference matrix is to add as many possible Dummy neigbours to get as many measurements as possible for your matrix.
You can run at OMC-R level the RMS application on one or more BSCs and collect the data, then you will build the Matrix into RNP. (RNP can build the Dummy neigbours for you with an add-in, you can then send ACIE files to OMC-R with PRC-generator)
Hope that help