Game Mechanics: /sit cause larger assist radius on rooted mob

[Scrubosaur]

Killing shadowed men....they con light blue so I root one which at that time does not aggro another that is close by. But when I /sit the one that was not aggro now aggros. This is all while at max casting range. It seems that the assist radius of the rooted mob got larger when I sat. I repeated this a few times to make sure it wasn't a once in a lifetime thing but it happened regularly.