SANTA CLARA -- Because the St. Louis Rams expect pass-catching dynamo Danny Amendola to return from a shoulder injury and face the 49ers on Sunday, cornerback Carlos Rogers is spending his practices gearing up for the challenge.
Or is it gearing down? Amendola is listed at 5-foot-11. So to give Rogers a good idea of what to expect, the 49ers' scout team is using safeties Trenton Robinson (5-9) and Michael Thomas (5-11) to impersonate the Rams slot receiver.
And if Amendola sits out?
"Then I'll be ready to go against another short, quick guy," Rogers said.
Either way, the Rams will be facing a tall order: The 49ers pass defense, a weak link a year ago, ranks among the NFL's best. The 49ers open the second half of their season No. 2 in passing yards allowed per game, behind only the Pittsburgh Steelers.
And it hasn't mattered whether it has been a jitterbug such as Victor Cruz or a hulk such as Calvin Johnson. Nobody is running loose in the 49ers secondary. They are one of three teams not to have allowed a 100-yard receiving game.
"(Defensive backs) are taking on the challenge of trying to match what the guys up front do in terms of stopping the run," Rogers said, referring to the 49ers' historically staunch rushing defense.
The 49ers are allowing only 184.0 yards passing per game, a 46.9-yard improvement from a year ago when they ranked 16th in the NFL. Opponents are managing a league-low 5.83 yards per attempt against them.
According to the team's media relations staff, the 49ers secondary is venturing into historic territory. Here are a few nuggets from the team's research:
The improvement comes not from new faces but from old ones. Among the most improved players from a year ago is Chris Culliver, a third-round draft pick in 2011, who has excelled as the team's third cornerback.
"Chris has done a good job for us since the day he got here," defensive coordinator Vic Fango said. "We have high hopes for him."
The old guys are getting better, too. Dashon Goldson, a sixth-year safety coming off his first Pro Bowl season, is playing with an increased awareness, according to coaches and teammates. Rogers pointed out that Goldson's anticipation skills are such that he can line up in a Cover 2 defense -- maybe 15 yards off the line of scrimmage -- and still come crashing in on run support.
"He'll stop the run after 3 yards, even from that depth," Rogers said. "He can disguise, because he's studying a lot more. It's helping him make a lot of plays."
Next, the 49ers secondary will try silencing a St. Louis passing offense that ranks 24th in the NFL. Quarterback Sam Bradford will get a boost from the anticipated return of his go-to receiver. Amendola was averaging 9.8 targets per game before sustaining a shoulder injury on Oct. 4. Despite missing the past three games, he leads St. Louis in receptions (32) and yards (395).
Rogers said Amendola ranks with Cruz among the league's top slot receivers; Fangio compared him to the New England Patriots' Wes Welker.
"Real quick. Real shifty. Tough and runs well," Fangio said.
If there is one thing in the 49ers' pass defense to nitpick, it would be the lack of picks. They have only six interceptions (far behind the Chicago Bears' 17). Overall, the 49ers have a ho-hum 12 takeaways, lagging far behind the Bears (28), the New York Giants (26) and the Patriots (20).
Rogers is aware of the numbers but is unfazed.
"Turnovers are great, but if you're getting a lot of three-and-outs and getting the ball back that way, that's good, too," he said. "We're not going to jump a route just because we didn't have as many turnovers as we had last year."