Ferrari brought a new floor to Suzuka in September in a bid to improve its aerodynamic efficiency.
The revamp featured changes to the front floor fences, floor edge, mid floor and diffuser sidewall, which worked in unison with a revised sidepod undercut.
The Scuderia's efforts to reduce drag also allowed Leclerc to be more comfortable in the SF-23, after team-mate Carlos Sainz had taken over from the Monegasque as the team's lead driver after the summer break.
While the update itself wasn't worth a huge amount of lap time, it allowed Leclerc to lean on the car harder, which saw him regain the upper hand on Sainz with three podiums and three pole positions across the final five race weekends.
"We had a small upgrade in Japan and I don’t know in terms of pure performance if it was something bigger, but I think in terms of comfort it was important and very beneficial for Charles," Vasseur said.
"I think Charles was in a much better shape in the last part of the season, the last six or seven races. This was a positive dynamic.
"I think we did a step a bit later on the consistency and the fact that we improved the car a little bit. That way we were able to be more consistent or have to push less in the race."
But as the battle behind Red Bull was decided by tenths, with Ferrari narrowly losing out to Mercedes in the fight for second, Vasseur didn't want to overstate the performance swings between his two drivers or indeed the rest of the frontrunners.
"Sometimes it is a matter of details. At the end of the day we are speaking about tenths of seconds, and from one weekend to the other we have to accept that they are sportsmen," he explained.
"[Roger] Federer can win one day in Wimbledon and lose the next, so I am taking them always as sportsman, up and down.
"What is true in our business today is that if you have a look at five years ago the Mercedes guys could miss one corner and still be on pole position. That is not the case today, you miss one corner, you are out in Q1.
"If you look at the two McLarens, they were out in Q1 [in Las Vegas] and they were able to fight for pole [in Abu Dhabi]. This is true for everybody except Max [Verstappen] probably, but it is true for Checo [Perez] and it means that we don’t have to draw too big a conclusion after one change."
