Hi Sacha,
This is a great question/issue.... I have the same problem with promoting posts to Facebook...every time they want money from me for reaching the full capacity of people .... still don't know a way HOW TO reach all the people .... Following this post :) Thanks a lot for sharing this interesting question :)
I can't see a way around it, other than continued posting and hoping to one day rest everyone!! Followed you and looking forward to your posts :-)