Ahh, my mistake. Sorry about that. Yes, charging from 1-50 I believe is supposed to be quickest part of the charge, it may slow between 50-80, but it definitely slows at 80-100. Read an article on this previously, but can't for the life of me recall the specifics on the "why" behind it.
Not having an 8 or X I haven't had the opportunity to use wireless charging. But I know in a previous update they added the ability to charge at 7.5w wirelessly correct? The output from a USB port is supposed to be 5w, maybe they're tweaking a behavior that wasn't intended where too much power was being drawn from a USB port? Just an idea. Maybe try with the wireless charger connected to a wall outlet with something providing more than 7.5w and see if the issue persists? Again, just an idea.