Last season Grosjean was Haas’ only points-scorer as Gutierrez struggled to get up to speed.
The Mexican racer was dropped after one season, replaced by former McLaren driver Magnussen.
This has seen a more even competition with Grosjean leading the qualifying stats seven to four and scoring 18 points to his team-mate’s 11.
Asked how Magnussen’s arrival at Haas had impacted on Grosjean, team boss Steiner told Autosport: “He reacted very well. I think he took it down as a challenge.
“Maybe at the beginning he was maybe out of his comfort zone but I think they get the best when they are just a little bit out of their comfort zone because when you are in the comfort zone you stagnate.
“You get complacent. It’s very easy to get complacent if you’re not challenged. Especially in any business or sport where the performance level is high.
“You need always to get a little bit pushed because otherwise if you’re too comfortable it’s always too easy.”