You can change the number of quests required to advance the tier, and possibly the value of the quests when you complete them, through xml - but I think the number of total points needed for the next tier is setup as a calculation based on the quests required per tier and the difficulty value of the tier in question.
Vanilla Settings
- Quests per tier - 10
- Tier 1 - 1 point per
- Tier 2 - 2 points per
- Tier 3 - 3 points per
- You get the picture
So the game calculates 10*1 = 10 points for tier 2 advancement, 10*2 = 20 points for tier 3 advancement
If you changes quests per tier from 10 to 7 (A21 setting), then it would be:
7*1 = 7 points to Tier 2, 7*2 = 14 points to Tier 3