I was once told by Tier 4 Avaya engineer that the algorithm for each loand on CM3 behaves differently for Medpro resource. We had an issue where the dedicated medpro for witness was being used for normal voice because the IP Network Region it was assigned was lower than the PN network region. I increased this value for the Witness Medpro, and voila, the resource got distributed to the PN correctly. So the answer to your question is, nobody but the developers will know exactly