You are going by career high ranking that was in the past, you should be going by current form, it's based on him having the most talent and ability of the 3.
Except the current form argument works even less in Pospisil's favour. Pospisil hasn't won two matches in a row this season and before today had actually lost two straight first round qualifier matches against players ranked far worse than him. He's actually in the worst form of the three at the moment (and lost to Dancevic just last month). If you want the player in the best current form to be the #2, that would be Levine as he's clearly played the best of the 3 in 2013.
Again, I ask, if he hasn't reached the heights of either Dancevic or Levine on tour and he's not playing anywhere near as well as them right now, what exactly makes him the "best" player?