Understanding TightKnit Analytics: Engagement Rate and Channel Insights

Hi! My VP is wanting to dig into the TightKnit analytics with me for our community and the definitions etc. specifically, the engagement rate. I know it’s relative to the channel, but how is the relativity determined? And if we added channels later to TightKnit can those be added retroactively? So that its more accurate for us? The prior teams didn’t add TightKnit when starting a few channels, but I’ve since made sure any new channels add TightKnit first.