In order to get the second Prestige Point you have to record two successes from a very small list. At the high sub-tier one of the possible successes only comes from the optional encounter, so if you don't have time to run it because of the fun roleplay then they MUST go two-for-two on the other objectives in order to get the second Prestige Point. If they don't have someone good at Bluff one of them is very, very difficult to boot. Sub-tier 1-2 has one extra way to get their second success, so it seems that they are more likely to get the second PP than sub-tier 4-5!
Bottom line, in the future I hope the Developers avoid having a Prestige Point success condition tied to the optional encounter!