Over the past three races, Russell took a fifth and two sixth-place finishes, while team-mate Lewis Hamilton grabbed a podium and two fourth-place results, as Mercedes battled McLaren and Ferrari for the status of second-fastest team.
Since the Austrian Grand Prix weekend at the start of July, Russell has said on several occasions that "things aren't clicking" between him and the W14.
When team boss Toto Wolff was asked about Russell's dip in form, he said the difficulty of finding a sweet spot in this year's car has affected Russell.
"These cars are on the knife-edge, and you can quickly fall off it and lose the confidence," Wolff said.
"And on the other side, if you're within that corridor of a sweet spot - although having said that, that car has no sweet spot - but being more in that zone of understanding what it will do next, I think there's a big difference."
Chief technical officer Mike Elliot concurred that the need for this era of ground-effect cars to be run close to the ground makes it harder to maintain the right balance around a lap.
"I think these cars are hard to drive when they're running close to the ground," Elliot added.
Source: Autosport