J/X Head exhaust flow?

I haven't heard much at all on exhaust percentage flow until I watched the video about camshaft selection in the link to my vintage iron. There is a bit in there about exhaust flow percentage. Personally I think it makes a lot of sense. The more exhaust you get out the more air/fuel mixture you can get in on the intake stroke. Definitely not stating that exhaust is of greater significance than intake though.