And other missing detail relates to crash testing, with Halo to be among the strongest parts of the entire car.
The missing details mean that, at a crucial stage of development of the 2018 cars, the teams are nervous.
"We have to get the Halo on the car for next year and that's a big challenge," Renault technical director Nick Chester said this week.
"That will be a big deal as it changes the chassis construction."
However, while president Jean Todt said he is open to considering different solutions in the future, the FIA is determined to press ahead with Halo for 2018.
"It was quite a late decision compared to the project but because of the safety it's important everybody tries to work very hard on it," said Ferrari technical boss Mattia Binotto.
"The implications are from the chassis structure point of view," he added. "So we need to make sure that we are fitting the Halo well on the chassis and the chassis resists the loads that are required by the regulations.
"Also from an aero point of view it will certainly affect the back of the car and that has to be taken into account when designing the new car," said Binotto.