The Classic Cup has been a graveyard for favourites and three times John Size has won it with surprises but Hong Kong’s form trainer isn’t expecting “that kind of race” this Sunday.

As the four-year-olds step up to 1,800m in this race each year, many are stepping into the unknown, stretching beyond 1,600m for the first time in their lives, while others are moving back into their comfort zone from their overseas careers. That may be a contributing factor to only one favourite having won the race in its 10-year history.

Odds-on favourites like Able Friend, Beauty Flash and Lucky Nine have gone over in it, their later careers showing why they were tested at 1,800m and Size has clobbered punters with Unique Jewellery at 11-1, Thunder Fantasy at more than 20-1 last year and the daddy of them all, It Has To Be You at 125-1 three years ago.

“Nobody really knows how far they’ll run until they prove or disprove it. It’s not something I angst about – you try them and then form an opinion afterwards whether they have had a proper chance to run it or not,” said Size, who has Classic Mile winner Sun Jewellery and Eastern Express in the race.

“But as for the upset aspect, well, I won it each time with horses I thought were ridiculous prices because they were going really well. Unique Jewellery ran favourite in the Classic Mile and had an excuse, and It Has To Be You and Thunder Fantasy also had tough runs in the Classic Mile that had to be overlooked but there wasn’t much wrong with their form otherwise.

“From that scenario, you’d be looking for the horse to cause an upset which was back in the field and unlucky in the Classic Mile but there wasn’t one. We know racing isn’t always as simple as that but the first three sorted them out pretty convincingly in the Classic Mile so this looks the kind of race where you’d expect them to run first three again.”

Sun Jewellery goes in with the distance query and also looking to be only the second Classic Mile winner to win the Classic Cup – Floral Pegasus did it in 2007 as the only successful race favourite – but Size also introduces new form with Eastern Express.

“He’s already won well at 2,000m, distance isn’t an issue but his handicap rating is well below some of the others and the race might just be coming too soon,” he said. “He’s a bit immature, not unexpectedly as he’s a June northern hemisphere foal, but so far that hasn’t held him back, he has acquitted himself well so we’ll try to qualify him for the Derby. “