Originally Posted by EpsilonZer0

Going from PP to Polaris has a much higher chance than going from Economy to Polaris but it does happen. Status level then Fare Class is how it is calculated.
Currently Platinum and I made the mistake of booking Economy and then using points shooting for Polaris only to wind up with PP. United does not differentiate the number of points used which really sucks.
However if you booked PP and trying to upgrade to Polaris on an international route it only costs 30 points instead of 40 points I found. Not much savings but it does work out to one more upgrade after 4 flights.