Just a quick update...
The GS6 flat and GS6 edge charge with normal operation on the mat. The GS6 edge + and the Note 5 both try initiating the charging however, it appears the device is just large enough that it doesn't rest completely against the pad thus hindering the charge from continuing. I get the green lightning bolt on the Denali's display but nothing from those two devices. Seems like the Denali initiates the charge but the device doesn't acknowledge so it stops.
I have a GS6 edge + and it consistently works for me. It just has to be placed with the bottom of the phone on the rubber stop by the end of the mat.