Hey Jason. Yeah I don't think the stock Reaper compressors has a side chain function on it. So you're not actually routing any tracks to a side chain compressor like say how a kick and bass get side chain compressed to get out of each others way?
Oh bloody hell I found one I downloaded awhile back that has a sidechain knob *slaps self* It's called Nova67P which is a free VST. I haven't really used it cause it looks complicated but I played with that sidechain knob and it shows where the slope is and you can dial it in to where you need. I'm gonna have to go back to Katie's track and test that out.