Charlottesville and Harrisonburg were indeed one market for a short time back in the 1980s IIRC. It's hard to understand why they would continue to be two markets, when they could easily combine into a larger one. Right now, WHSV has to cobble together four networks with a mix of subchannels and LPTVs, moreover, I'm pretty sure their NBC station simulcasts WVIR's newscasts. There would be issues with the terrain --- Charlottesville stations couldn't easily be received in the West Virginia counties, WHSV has enough challenges with the mountains separating it from Pendleton, Grant, and Hardy counties, and as of 2018 (most recently publicly available Nielsen map), the latter two counties were assigned to the Washington DC market anyway.
Dumb question, is it necessary to have a set number of markets? I'm confused by the suggestion that adding the San Juan market would have to be compensated for in some way.