Ok so today....

level 44
Started with 9,284/390,800 got to 54,176/390,800. 45% Bonus would be 175,860. And I got 44,842 EXP from Mob kills.

Bonus was 186,503 which is close to 48% + the 4,632 for boss kill took me to 245,311/390,800

So EXP from Mob kills don't count toward the Bonus.