I have a Zephyrus M16, and it has a huge gap of 1.6 mm on the right side when the screen is closed. 0.7mm on the left. The top edge is mostly flush, but lifted 0.4mm on the right corner. Sigh.
At the store I bought from, the display model had a huge gap on the top edge when closed (3mm+), which tapered down at the left and right corners.
My unsolicited opinion is that Asus chose a poor magnesium alloy for the chassis and/or did not properly thermally treat the material in the manufacturing process.
Whatever the case, I will be modifying my lid so that only a cm of the original lid remains (the part with the hinges), cold-welded to a solid aluminum lid from a Dell XPS 15 9500 (which happens to have just the right width, while being a little shorter in length than the M16 lid). That is, after I sacrifice my big toe to the roman goddess Fortuna in hopes she will prevent my LCD from being utterly destroyed as I foolishly try to pry it off the factory lid.