Question for this... From what i've seen, the rested exp bonus builds over time while sitting in a sanctuary or inn. My question is when switching classes, does this bonus scale accordingly?

IE. i'm resting on my lvl 20 class right now and say it's bar is currently at 50% for rested exp bonus. I switch to my lvl 5 class. What i would expect is for that bonus exp to scale with the exp required. Can anybody confirm if the rested xp is a percentile growth on the xp bar, or if it's actually exp related?