Pedro Caixinha reckons Rangers' foreign recruits are beginning to show their qualities now that they are settling in to life in Scotland.
All three played key roles as Rangers won their last two Premiership games.
"All of them needed different times to get adapted. It's a different reality, a different culture," Caixinha said.
Pena and Herrera have had less game time since arriving from Guadalajara and Pumas respectively, but the former opened his account against Dundee after Herrera did the same in Dingwall.
With the likes of Daniel Candeias also coming to the fore in recent matches, Caixinha believes his summer buys are now getting up to speed with life in Scotland on and off the pitch.
"Even for me as a European from Portugal, it's different coming to live in Scotland," Caixinha added.
"Imagine what it's like for someone from the other side of the world to get adapted to this culture, this type of football.
"For example, the guys from Mexico find it unusual to play all the time with the pitch wet. That gives you more pace in the game and they need to understand that.
"However, they're now getting together in the direction we want.
"We've brought their families over, found them a place to live, found a college for their kids, but there's still other adaptations, like food and nutrition. So there's lots of things to think through and get together for them to feel comfortable and confident. Then they can express the football they have."
Caixinha was happy to see Pena show glimpses of what prompted the club to pay £2.5m for his services, with the Mexico international coming off the bench to smash in the third goal against Dundee in a 4-1 triumph.
"Against County and Dundee when there was more space because we were leading, Carlos felt free to perform," the Rangers manager added.
"But now we're preparing him to understand sometimes the time and space isn't there.
"That's the question we need to go a little bit further on, to the next level, for him to perform with us on a regular basis.
"He's going to get the rhythm by playing in the match, not by training. The training is not going to improve him - the match makes the difference."
Rangers visit Partick Thistle on Friday night and Caixinha hopes to see a real hunger among his players as they look to make it three league wins in succession.
"The players aren't satisfied when they win a game 4-1," he said. "I wasn't happy and that's the mentality we need to spread.
"Yeah, we won 4-1. OK, it was a good result, a good performance in some moments but we need to improve in others. That's the reality we need to face and always be thinking we can grow as a team."