umm, no, that is not how it works
you will always get the 20% of the base xp
so if a camp gave 100 xp
scout buff would give 20xp
mary gen give additional 100xp
and 30% gen skills give 30 xp
so added together you get 100+20+100+30 = 250xp then add prem
without the scout buff you get 230xp, so the increase seems like 8%, but the scout buff % is based on base xp not overall xp