I'm not saying hes been Vonte Davis bad, not at all. But on that TD to Mike Williams, they specifically went after him. Rivers said it after the game. Davis was the corner on that play (doomed from the start), and Poy-yay was in position, but he couldnt make the play regardless.
And his run support last year was awesome. Alot of plays at or behind the line of scrimmage. This year it seems like hes 5yds deeper, meaning he has to make an open field tackle or get the RB with a full head of steam.