Red Bull's Dr Helmut Marko said after Montreal that Honda, Toro Rosso's engine partner, stepped forward to the tune of "three tenths" in Canada.
Yet Renault, willing to remain Red Bull's engine supplier beyond 2018, says that it also improved.
"The improvement since Melbourne has been three tenths, including 1 tenth thanks to new fuel introduced in Barcelona," Remi Taffin told France's Auto Hebdo.
"It is the equivalent of about 20hp, which is in line with our expectations. We are already working on the next evolution, which will take place after the summer factory shutdown."
Renault, though, is refusing to wait for Red Bull's now long-delayed decision.
Red Bull says that it wants to wait until Austria before making an announcement, but Cyril Abiteboul says that is too late.
"We have extended the deadline due to the 12 years of good cooperation that we have had," he is quoted as saying by Marca.
"In Montreal they saw our new specification and that of Honda -- they have all the information. I see absolutely no reason to delay this further.
"In Austria, our offer is not going to be there anymore and they'll have to talk to Honda. Our offer has to be accepted in the next few days."
Taffin, Renault's engine technical boss, said that the tension between the French marque and Red Bull is understandable.
"You have to be pragmatic," he said.
"It's been 12 years that we work together, winning a lot of races and world championships.
"We always talk about someone who said something, but we must not forget the 600 people in Milton Keynes and the 400 in Viry-Chattilon. They all get on well, so we have to put that at the centre of the game."
The 2018 season continues next weekend with the French Grand Prix.