I’m actually surprised your charger is flashing green. Mine still flashes orange on the latest beta, without a case, and at ~40% battery. I’ve reached out to RAVPower.....again..... about their claim that they support fast charging on the 8/8+/X. If I remember the Macrumors article correctly, it was RAVPower that contacted Macrumors about the latest beta enabling fast charging.
https://www.macrumors.com/2017/11/14/ios-11-2-faster-wireless-charging-iphone-x/
I may have spoke too soon. Last night the charger only flashed orange and not green. Might have been a fluke.