Correction, I see the Y signal you used is 126. For example, the R value for the B-Y patch is 126, coming completely and only from the Y signal. But if you want to stay within legal limits of RGB ranging from 0 to 1, you cannot reach 100% saturation with 126 visual brightness if the hue is bluish. So for the 40% saturation B-Y patch, you added a lot of blue and subtracted less R and G to keep the Y signal at 126.