However, the Spaniard says that the direction the team has taken has also made him more comfortable with the car over one lap.
Both Sainz and his team-mate Charles Leclerc faded badly in the Saudi Arabian GP after pitting for the hard tyres and eventually finished sixth and seventh.
The team has spent the days since then investigating the issue and came to Melbourne with some potential solutions in terms of set-up.
It also opted not to bring any aero updates, which meant the SF-23 was a stable platform from the last race and the team could more easily make direct comparisons with Jeddah while focusing on set-up.
Ferrari had the second fastest car behind Red Bull in qualifying in both Bahrain and Saudi Arabia, whereas in Australia it slipped to fourth in the pecking order, with Sainz qualifying fifth and Leclerc seventh.
"Obviously I cannot go into detail but we've decided to take a different approach this weekend trying to improve the race pace," said Sainz when asked by Autosport about the team's strategy.
"And I've no idea if we have done it or not, because the real test comes tomorrow. We've definitely changed the car on the set-up, and I'm hoping it will pay tomorrow."
Sainz stressed that he felt good in the car in qualifying with the new set-up, despite the aim being to make the car better in race trim.
"Yeah, I'm reasonably comfortable," he said. "I think we've done some good progress with my feeling with the car. We've changed quite a lot, the set-up, up and down from yesterday, trying to improve it mainly for the race.
"But, actually, the changes have made me feel a bit better also over one lap. Unfortunate that we couldn't prove it today, because I lost a couple of tenths in sector one in that final lap that cost me a top three that would have maybe been a boost of motivation for me and the team.
"But we missed it due to a very poor preparation lap. They told me there were people coming on a fast lap. Some of them were, some not. I cooled down the tyres and it cost me a lot in Turn 1."
Sainz conceded that it helped not to have new aero parts on the car that might have confused the team's quest to solve its problems.
"Especially when you have three weeks after stopping, I think it's better to experiment with set-up and be very clear what is the direction that we want in the wind tunnel and in the car to improve," he said.
"This is why we are right now experimenting and waiting to see the clear direction to go in the future."
Regarding potential race form, he added: "A big unknown, wishing that tomorrow will pay off. But I hope that I can keep the pace of the Astons and the Mercedes and fight them.
"If we fall back, it means that it's like in Jeddah where we fall back a bit. But we're trying the best we can."
