Phil Smith, head of handicapping at the BHA, reports Sea The Stars ran to a mark of 131 in the Qatar Prix de l'Arc de Triomphe at Longchamp on Sunday.
That's four pounds below the rating he achieved when winning the Irish Champion Stakes on his previous run.
"You don't get horses winning Group Ones in six successive months every year. That was very special on Sunday. Everytime you put opposition in front of him he beats them and is an absolute tip-top horse," Smith told At The Races.
"In terms of ratings we've left him on 135, which was the mark we had him performing to in the Irish Champion Stakes."
Smith revealed 131 was an easy rating to reach for the Longchamp performance.
"We looked at the Arc and there were pretty good yardsticks in Youmzain and Conduit in second and fourth, there are fractions between them. We have them both performing to 125. Youmzain had been placed in the race twice before and we had him running to 124 in 2007 and 125 last year .
"Conduit was rated 125 in the King George and America last year so we've rated the race through them. We call the winning distance more than two lengths given the ease of victory and we've called that six pounds so we've given Sea The Stars a performance figure of 131. That's all he needed to do to win the race. I suspect he had something in hand."
Smith admits Sea The Stars could achieve an even higher rating before the end of the year - even if he doesn't run again.
"We're still not sure we've got him as high as we can get him. Rip Van Winkle will go off to America and if he goes higher there then Sea The Stars will go higher," Smith confirmed.
"Our 135 is only an interim performance figure - if the form continues to work out there's no reason at the end of the year when we meet in Hong Kong we can't get him higher. 135 is the absolute minimum he will be at the end of the year."