Charles Leclerc struggled not only when switching from the hard compound tyre to the medium, but even with car balance from lap to lap.
The Spaniard had started third but fell back during the race, especially after switching to harder compound Pirelli tyres.
“I think the pace was decent but we are not able to put everything together,” said Vasseur.
“The first stint went pretty well for Carlos, he lost a couple of seconds on one-third of the race, and he lost 25 seconds in the last two-thirds.
“We were far too inconsistent from one car to the other, and from one lap to the other. We have to understand why.”
“The first stint on mediums for Carlos, he lost five seconds in 18 laps,” Vasseur explained.
“I think at this stage of the race was okay for us.
“Charles was the opposite. He was in a good shape at some stages of the second stint with the hard; he was struggling much more on the first part of the race.
“We really need to focus attention on this because that is the key for us,” Vasseur reaffirmed.
“I think for Charles we were more performant on the hard; with Carlos we were more performant on the medium.
“And even with the same tyres, from one lap to the other one we are a bit inconsistent.”
Speaking after Sunday's race, Leclerc lamented the lack of consistency he felt within his car, citing differences from lap to lap in the same corner.
It follows two more events for the Scuderia, with Leclerc scoring the team's first podium of the year in Azerbaijan.
There was better performance in Melbourne, too leading the team to believe it had made a step forward.
After five races in 2023, it sits fifth in the constructors' championship on 78 points, already 146 behind Red Bull.