Yes, XP is based on the character's level, however there is an XP cap for tasks, according to the chosen difficulty:
- Beginner: 200,000 XP
- Adept: 800,000 XP
- Expert: 3,000,000 XP
- Mastery: No cap
CipSoft did not disclose the formulas used to calculate XP. But I believe the formulas are as follows, according to the chosen difficulty:
Beginner/Adept: XP (L) = 25L² - 75L + 100
Example: XP (Level 40) = 25x40² - 75x40 + 100 = 37.100
Expert*: XP (L) = ~1994 x L
Example: XP (Level 596) = ~1994 x 596 = ~1.188.424
*But apparently this formula only works up to a certain level, which I don't know. At my MS 1375+, I already gain 3 million XP.
I don't know the formula for Mastery difficulty, as I haven't chosen that difficulty with any of my characters yet.