URF MODE vs Regular Mode Participation Rate

Just something I was thinking about when playing URF and then observing my friends list: I noticed that 80% of my friends were playing URF, so I was just curious of what the participation reduction in normal SR is when Riot enables URF mode. I personally have a tough time getting back into normal mode after playing urf as the game feels (and is of course) soooo much slower and actually kind of boring.