It is all, it seems, in the tweaks. So said Aidan O’Brien, Ireland’s master-trainer supreme, before his tough filly Magical defeated Ghaiyyath, the world’s highest-rated horse, in the Irish Champion Stakes on Saturday. He wouldn’t have run her against the relentless galloper who had beaten Magical the month before, he insisted, if he hadn’t felt there was something he could tweak to make the difference.