While Randy Moss and Mario Manningham have created a much bigger buzz on offense, 49ers team insiders believe fellow free-agent addition Perrish Cox very well could become an equally valuable contributor on the other side of the ball. Close observers of the Niners’ offseason activities agree that, aside from Moss, the versatile Cox has been the most impressive performer. “We like Perrish. We’ve got him playing nickel and corner, which is two different positions,” Niners defensive coordinator Vic Fangio said of Cox, who did not play last season after getting arrested in December 2010 on a sexual-assault charge and being cut by the Broncos right before the 2011 season. “He’s done well learning those positions, and we’re very happy to have him. He’s given us added depth, and he’s going to push for added playing time if he continues the work that he’s showing so far,” Fangio added.