I've come to the conclusion it is a function of the slant of the windshield and how near/far you are to the windshield. Driving home today in my 2014 535, i can see the HUD with my sunglasses (polarized) much better than on my 2016 X5. The windshield in the 535 is much more slanted than the X5, and I think (not actually measured this) that I sit a bit closer to the windshield as well.
Yes, in the X5 I do the head tilt, slide the glasses off thing. No need to do so in the 535.
And of course, they both work wonderfully at night, where the HUD really "shines" (pun intended).....
I think it's all in "the angle of the dangle"
