Big-race genius Craig Williams has supplied the tip of the spring so far with his praise for Cox Plate "war horse" Green Moon.

"If I wanted to go to war with a horse, I'd go with Green Moon," Williams said.

Williams, who won last year's Cox Plate on Pinker Pinker and who last weekend made it back-to-back Caulfield Cups on Dunaden, said he couldn't be happier with his late decision to switch from the favourite Pierro to Green Moon.

He said it hadn't been a difficult choice.

"On the work he did eight weeks ago I felt Green Moon could win," he said.

"I was given the opportunity to ride him at the last minute and I'm very happy."

Williams's glowing endorsement of Green Moon preceded a typically stunning performance by trainer Gai Waterhouse at Tuesday's Cox Plate barrier draw.

Given the option of selecting whichever of the 14 barriers she wanted for the high-class mare More Joyous, Waterhouse prompted incredulous reaction by choosing No.11.

"The reason is there might be some squeeze barriers and it just gives her that little bit more room to move," Waterhouse said.

"There were 14 barriers to choose from and I chose 11."

A more traditional approach was made to the barrier selection for the favourite Pierro who will jump from gate seven while the third Waterhouse runner Proisir was left with little choice but to accept 10.

Green Moon, the second favourite, drew perfectly in barrier five with third pick Ocean Park to jump from nine.

Waterhouse was also at pains to justify Pierro's Caulfield Guineas second placing, claiming the colt had lost nothing in defeat and that, he, like all her horses, was "110 per cent fit" and would be suited by the 2040m of the Cox Plate.

"He's a really outstanding horse, I don't think he lost one admirer the other day in the Guineas," she said.

"I think the distance will suit him better and I think the way the race is will suit him.

"They are 110 per cent fit and I've just got the job to make sure they stay sound and happy."

The Waterhouse praise for Proisir was similarly unbridled.

"This is his first preparation," she said.

"You tell me any horse in Australia that's got to weight-for-age, the leading weight-for-age race in Australia, in one prep.

"It's unheard of."

Proisir held his position in betting at $9 while the curiously drawn More Joyous eased from $10 to $13 with Pierro tightening his hold on favouritism at $4.

Despite the disparity in the betting, Waterhouse declined to split her trio.

"I'm their trainer ... I'm mother," she said.

"I want them going into the race with a lovely disposition, and they've all got that."