SHANGHAI, China -- Red Bull boss Christian Horner has called for clarity over how drivers are allowed to line up in their grid slots after Ferrari's Sebastian Vettel failed to park his car between the lines at the Chinese Grand Prix.

Vettel started from second on the grid but positioned his car way to the left of his grid box, ostensibly to avoid oil and wet patches on the run down to Turn 1. In the end he made a relatively poor getaway regardless of the positioning, but he still managed to hold Valtteri Bottas off on the entry to the first corner and retain second place.

The same issue was discussed at the driver briefing at last year's U.S. Grand Prix after Daniel Ricciardo positioned his car in a similar way on the Japanese Grand Prix grid. Following that incident Lewis Hamilton called for clarity on the issue and Horner believes it should be addressed so drivers know what is allowed in the future.

"I believe that had been previously discussed," he said. "I think the one thing that would be nice to come out of it is... because it was obvious what he was trying to do -- get to the drier part of the track which you can understand -- but it would be good to have clarity of does a driver have to start in his grid box or not.

"Is it just a line or is it a box? I remember it being discussed, but he got no advantage from it. It would just be good to have clarity."

The stewards investigated the Vettel incident but decided not to take any action.