
Grundle the Trundle |

I am having a hard time finding a source for a ruling. I am playing a character that heavily focuses on grappling (took the wrestler archetype and everything). My character's ideal strategy is to tumble through the front-line and use their high speed to make it into the back-line and grapple a caster or other high-value target. We go through an encounter and I find myself in a position to do that very thing. I get a nat 20 and critically succeed. While using the grapple maneuver, that means the target is restrained for a round. Another player reminds the GM that boss mobs (and this was the boss of this part of the Adventure Path) treat all status conditions as if they are one step lower (critical success becomes a success, success becomes failure, etc.) So instead of being restrained, they only become grabbed. They proceed to cast sleep on me and I fail the roll and am out of the combat for 5 rounds until someone wakes me up and everything is basically over.
This is the first time I have heard anything about "boss" mobs being able to shrug off status conditions. I am familiar with the **incapacitate** trait on abilities and how that interacts with higher level characters. The basic grapple action does not have this trait.
What I am trying to figure out is if this is a rule that is printed somewhere I cannot find or if it is a house rule designed to make boss encounters more threatening. The GM and other players at the table made it sound like it is an official rule, but I cannot find it anywhere. Any rules lawyers here able to provide a source?