The Dane qualified 19th for this weekend’s Hungarian Grand Prix while team-mate Nico Hulkenberg continued his strong one-lap form by running to 10th place in Budapest.
Magnussen blamed a 0.511s gap in Q1, when both cars were running with hard tyres under the experimental Alternative Tyre Allocation, on his discomfort aboard the VF-23.
He says that as the Haas car has evolved, he has struggled to find consistency in low-fuel and new-tyre conditions as the handling has moved away from his natural driving style.
“[I’m] struggling to find consistency with this year's car,” said Magnussen. “For some reason, I'm struggling a bit on low fuel, new tyres to extract the maximum out of the car.
“Lots of inconsistency for me and as you've seen in FP3, I had purple sector one and then I'm the slowest on sector two, so going very extreme there.
“It's almost like my usual strength have become my weakness in this car.”
Magnussen added that he was content with his long-run pace. However, this has been a particular weakness of Haas this season owing to its struggles to understand and manage tyre wear over a race stint.
Asked to explain why his old strengths were now working against him, Magnussen said: “It's my inherent driving style trends that are working against me at the moment with the specific limitations of the car.
“Nico is obviously seeming to extract more out of the car [over] one lap, new tyres. And then on high fuel, it's different story. So, it's a bit of a confusing one. But I'll work on it.”
Asked by Motorsport.com whether Magnussen had felt this downturn since testing in March or whether the car had more gradually evolved away from his sweet spot, he said: “I want to say the car's got better, but it's gotten worse for me, in terms of my specific driving style.
“It seems to be becoming bigger and bigger, the issue that I'm causing in the car with my driving style.
“It's hard to change some things in your driving style. You can change a lot of things, but some things are so natural and so automatic, it's hard to change.”
Discussing whether he could adapt based on the data from Hulkenberg, Magnussen reckoned that to follow the German too closely could leave him in "no-man's land"
He said: “I can see what he's doing and what the differences are. But some things in your driving style are really hard to change.
“If you change things that are very natural to you, you end up in no-man's land… the previous year's [car] has not been a problem. Now suddenly, I find myself in a bit of a pickle.”
