Toyota has warned against 'playing around' with the World Endurance Championship's new LMP1 success handicap system, which has already hit its limit.
The Silverstone-winning #7 Toyota TS050 Hybrid and the sister #8 machine were slowed by 1.4 seconds and 1s per lap respectively for the last round at Fuji but still took a dominant one-two.
Rebellion's solo R-13 was given only a negligible 0.03s a lap penalty under the new rules but could not keep pace with the Toyotas.
The handicaps were calculated using a revised co-efficient of 0.012s per point (compared to the last-placed LMP1 car in the standings) per kilometre of the track, up from the 0.008s that had been originally prescribed.
Toyota team director Rob Leupen cautioned against further adjustments.
"This was a bit of a surprise," Leupen told Autosport when asked about the co-efficient change.
"We accept it, but we also expected the pace of Rebellion [at Fuji] to be much higher based on where they were at Silverstone, so I hope they can come to our level.
"I think we say we should know what comes, because to put the car right for a circuit and set it up for a circuit, we cannot play around all the time."
The LMP1 handicap system continues to apply penalties up to a 40-point gap, a limit that both Toyotas have already reached in relation to the so-called reference car, the #6 Team LNT Ginetta, which has scored only 2.5 points in two races.
Rebellion's #1 entry, 11th overall at Silverstone and third at Fuji, is 27 points down, giving it a theoretical advantage of around 1.6s a lap over Toyota for the next round at Shanghai.
Leupen was clear the 40-point limit should be "respected" in the event that the privateers fail to beat Toyota even with the biggest handicap allowable in the rules.
"There must be a ceiling, otherwise we might get some difficulties running these cars because they need to have a certain speed, a certain recovery, and it's very expensive to start changing systems and we don't want to do this," Leupen said.
"For us it's a learning curve. In the next regulations we talk about BoP, which for us is the first time to race under these circumstances. It's never been done before.
"The engineers had a lot of things to do to put everything right with the car, the complexity is huge. But there is a ceiling and this we should respect."