Be nice. Or else.
I spent a long time trying to understand this also. Take a look at Google's device metrics for a full spec of the Pixel and Pixel XL.
Because of the screen size and the resolution built into each device (Pixel/1080p, XL/1440p) this renders both screens at the exact same 1x point size (Or Density-independent pixels as Android states it in their design spec)
I think the Icons will be rendering at different sizes due to each device registering as a different 'density' at render time...
There's not much we can do about that I'm afraid, try changing the display size on the actual device and it will adjust the layout into a different layout density...
I haven't worked on this for a while though, so i can't help much further but hopefully that sheds some light!
Thanks a lot for your comment! Makes sense indeed, especially when checking out that metrics chart by Google. We probably have to live with it right know, but it's pretty annoying not to be able to check out the pixel perfect designs. Too bad!