Could you please add another item to that request?
- Allow decals to be spawned on a translucent surface (such as bullet holes on glass, oil slick on water etc)
There were a few requests for this back in 2014 on AnswerHub that said it will be implemented, but I couldn’t find any updates on it (or any workarounds :(). If anyone knows of one I’d love to hear it! 
Thanks.