So Obligation is set for three players (15 points each). Each player then maxes out their additional Obligation with bonuses to XP and credits (+15 Obligation each). So Obligation for the group is at 90 with each player having 30 Obligation each.
A few sessions in, a fourth player wants to join. How do you adjust Obligation?
Looking at the chart, four players would have a starting Obligation of 10 each (with a potential +10 additional).
Do you have the fourth player come in with 15 (+15), which would make the group's total from 105-120, depending on new guy's choices?
Do you adjust everyone's Obligation down to 10 each because the chart says 4 @ 10? If so, then the original three players in retrospect got to "over spend" their additional starting Obligation. If that's the case, then it would only be fair to let the fourth player have up to +15 additional Obligation too, yeah? Then the group's total is from 85-100, depending on new guy's choices.