The dual Champion Chase hero is virtually unbeatable when on his game, but has thrown in the odd stinker over the past couple of seasons.
That was the case on Merseyside last month when he trailed home last of three runners in the Old Roan Chase, but Nicholls has reason to believe much better is in store.
“Fast ground, going left-handed, doesn’t really suit him and he was hanging out to the right,” he told Racing UK.
“He was big and well but I was targeting the races at Christmas and the spring with him and I was rushing him a bit.
“My aim is to have him at his very best for the King George.
“He’s improved enormously from Aintree, he worked great on Thursday. There is still improvement in him but that’s how I wanted to train him this year.
“I want him at his best on Boxing Day and that’s what I’m trying to achieve.”
It promises to be a huge day for owner Clive Smith, who will be watching Master Minded from Haydock, where Kauto Star lines up in the Betfair Chase.
“I think we just had him out prematurely at Aintree when he wasn’t fully wound up, but it’s very difficult to gauge a horse’s fitness until he’s had a run,” Smith said.
“Paul obviously gave him a try, it didn’t work out, but he realised what he had to do to get him right.
“I’m sure he’ll be ready to run his best at Ascot.”
With regular partner Ruby Walsh at Haydock, Daryl Jacob takes over riding duties on Master Minded.
“I schooled him this week and he seems in great form,” Jacob told At The Races.
“He’s obviously come on a lot from his Aintree run, so hopefully we go there fit, fresh and well and hoping for a good run.
“I’ve spoken to Ruby about it and watched the Aintree race myself. The ground was quick enough there. He probably just needed the run. He’s a real gentleman of a horse and knows what he’s doing.”