SANTA CLARA >> When Christian McCaffery is healthy, it’s not as if coach Kyle Shanahan is in a lounge chair, drink in hand at his favorite vacation spot in Cabo San Lucas while leisurely scanning his call sheet.

Shanahan sounded almost wistful last week when he talked about McCaffrey’s effect on play-calling.

“I feel it’s been as easy of football as I’ve had in my 20 years,” Shanahan said. “It’s a very good bonus to have a really good third-down back for situationally what it does on third down, what it does in the red zone. To me, it has as big an effect as I’ve experienced, but you don’t always have those guys.”

As he later conceded, Shanahan was exaggerating to make a point, as coaches are wont to do. Play-calling is never easy, and the 49ers have managed to be good on third down with McCaffery on injured reserve indefinitely with Achilles tendinitis affecting both legs.

Missing the NFL’s premiere running/receiving back has the 49ers only slightly behind their third down conversion rate of a year ago. They were fourth at 47.5% in 2023, and are No. 6 this season at 44.7%.

The red zone, where the money is made, is another story. After leading the league with a 68% touchdown rate (51 for 75) from the 20-yard-line and in, the 49ers are slogging along at 50% (8 for 16) through four games.

It’s an area the 49ers (2-2) will need to improve upon, beginning with today’s NFC West game against the Arizona Cardinals (1-3).

Place kicker Jake Moody is tied for third in the NFL with 11 field goals (in 12 attempts). But six of those have been of the point-blank variety when drives stalled in the red zone, including the last three inside the 10-yard line (one against the Rams, two against the Patriots).

“It takes 11 guys to do their job really well and for us to be on point when it comes to the throw and catch,” 49ers quarterback Brock Purdy said. “We haven’t executed at our standard and that’s why we’ve had to kick so many field goals. You learn throughout the season what it takes, and it’s not just given to you down there.”

For all McCaffery did for the 49ers, the 2023 NFL Offensive Player of the Year was at his best in the red zone. In the 33 games including the postseason McCaffery has played for the 49ers, he’s scored 39 touchdowns. Of his 26 rushing touchdowns, 20 were on runs in the red zone and 16 of those were from the 5-yard line or closer.

As a receiver, McCaffery has 13 touchdowns, eight of which were in the red zone. The average distance of a McCaffery receiving touchdown is 14.8 yards per play with rushing touchdowns averaging 9.7 yards.

His dual-threat capability creates a dilemma for any defense.

“When Christian’s out there, it’s easier in everything you do,” Shanahan said. “It helps you know what you’re getting a little bit more. Defenses know how good he is in one-on-ones so you expect two people to be there and it helps you in other places. It helps you know what you’re getting a little bit better.”

Jordan Mason is second in the NFL in rushing with 447 yards and leads the NFL with 91 carries. He has three of the 49ers’ red-zone scores on runs of 5, 10 and 4 yards. The others belong to Deebo Samuel (2-yard run), tight end George Kittle (7-yard pass, 12-yard pass) and wide receiver Jauan Jennings (13-yard pass, 4-yard pass).

A running back has yet to catch a touchdown pass through four games, although Mason (38 yards) and Kyle Juszczyk (7 yards) did have touchdowns called back due to penalty, a drive that ultimately ended with Purdy hitting Kittle from the 12.

While Mason worked in the offseason to improve his receiving skills, he’s been targeted only seven times and has six receptions for 57 yards. He hasn’t had as much experience with the “choice” option routes where he and the quarterback adjust the pattern based on the defensive coverage.

“You can draw up a play on paper, but when everything is live and it’s going full speed against another defense, there’s another component of understanding where you need to be and how you need to run your route based on leverage,” Purdy said. “For a running back out of the backfield, that’s such a big thing. Obviously Christian is probably the best in the league to do it. For (Mason) to jump in those shoes and try to feel it out, he’s done a great job. And it’s not easy.”