Vcore 3.1 500 IDEX

Think I got my frame square. The range of 0.255 mm is not bad, there is however still a saddle in X-direction. With advise from the attached YT I have already loosened and retightened lightly the x and y axis screw's and checked the rails for flatness. This makes no difference. Can this be further improved or is thsi the best I can get?