Kimi Raikkonen says the pecking order behind the top three teams is "a big mystery".
Some are predicting that Alfa Romeo is now ready to take on Renault to be the 'best of the rest' in 2019.
"It's unclear to us where we stand," Finn Raikkonen, who has switched to the former Sauber team from Ferrari, said.
He admits the 2019 car is a "solid package, but we still need to improve a few things".
"The mood is good and there is nothing negative, but like everyone else we want to improve. There is always something to improve," Raikkonen added.
Among the midfield pack is Haas, with its boss Gunther Steiner saying it would be "a dream" for the American team to finally end a race on the podium.
"But if everything goes well, nobody can reach the podium except for the top three teams," he said.
Sergio Perez, who drives for Racing Point, said: "We know we are not the fastest but not the slowest in the middle group of teams.
"At the same time, the difference between the fastest and the slowest of those teams is less than half a second," he added.
