I do not think so. According to this post
by the design lead for diplomacy, there is something called "degree of victory" that is added to a hidden counter and when a threshold is reached, you get the point.
No one is quite sure what "degree of victory" means, but the two leading theories are:
1. The total number of Dialogue Points left on your opponent. If this is the case, then you want to parley against the lowest skilled opponent you can find to maximize the points you can earn. If this is true, you want to parley against people 50 points in skill below you, or more, so that you can have upwards of 30 dialogue points left on the bar when you win.
2. A minimum of Dialogue Points lost over the course of the parley. If this is the case, then you want to parley against the opponent where you will lose the fewest points. If this is true, then there is no difference between giving up one Diallogue Point to a higher skilled or lesser lesser skilled NPC.
Either way, if player analysis of Aruspex's cryptic statement is correct, relative skill level of PC to NPC has no impact directly, only the number of Dialogue Points matters in some manner.