GM wireless charging has 2 major issues.
#1 GM pad thickness is almost 2mm thick, this greatly reduces charging capability,
especially if your using a case. I removed the GM pad and replaced with a thin leather like material.
#2 problem physical size limitation, for newer phones and cases, the sweet charging spot is further back on the larger phones and you will need to move the position all the way to the back edge.
If you remove the bezel the rubber pad will lift out and you can trim to fit.
max. phone/case width 3.1 inches with Gm pad removed. I now can charge my S8Plus with the phone case, installed no problem.