you have 2 distinct problems with wireless charging in GM vehicles.
I use a S8+ with a case, and charge wireless in my 2017 Tahoe.

#1 the GM pad is almost 2mm thick, this makes wireless charging difficult and less effective.
I replace the rubber pad with a leather like material, minimize this thickness.

#2 the charger is installed to far forward for larger, (S7-S8/Note) phones to charge.
If you remove the outer bezel you can see how to remove and modify the charger Pad to accept larger phones,
maximize phone width 3.1 inches. by moving the charger position all the way to the back of the Bezel.
as a bonus I added a led so the White edge glows when phone charges.