Tom, I am not sure what you are referring to as actual numbers in your 11%. Since the vector from D65 to REC709 Red (.640,.330) is .327, an 11% error would be .036. From that lets say Red is .670, .330 (x,y). Now, it is said a color error of .004 is visible. From that, .327 is 900% of a potentially visible error.
Now for luminance, say Red is supposed to be 15fL, the 11% error would be 13.35fL. At a gamma of 2.2, that would be the difference between 100 IRE and 95 IRE.
Now if you put your blocks on a screen with some separation, say opposite corners on a black, gray, white field, you could see the color difference, but might not be able to see the luminance difference.
I don't think you canuse a direct correlation to the digital 0-255 colors and luminance to what you see on a video display with respect to color space and luminance without the effects of signal and gamma. This is because if you use 11% luminance as a difference in linear digital 255 > 227 is about 11%, however digital 227 signal with a gamma of 2.2 would be about 11.6fL = 22.6%
The when we view on our PCs, no telling what gamma is in use there.......