Liberty Media is "really satisfied" with the research that is being done on the car concept of 2021.
It is believed most of the teams are now willing to wait until October for the concept to be finalised, with Pat Symonds leading the efforts for F1 owner Liberty.
"We are really satisfied with the basic concept," he told.
"The numbers for the car that is following are better than we expected."
One reason for the hold-up, he explained, is that his team that is coming up with the concept is trying to imagine how the F1 engineers will work their way around the overtaking-friendly ideas.
"They logically have only one goal: to make your own car as fast as possible. They're not interested in the car that is following.
"So we are trying to imagine how these engineers could outsmart our design so that we can close those loopholes," Symonds, an experienced F1 engineer, added.
