Don’t know if this is new info (probably not) , it is new to me, although I was kind of suspecting it after seeing ambush applying to pretty much anything during deception (unforseen , kunai impact and splashes, …) .
The grenade(s) doesn’t have to be thrown during deception … one can throw tesla/corrosive cloud/fire burst AOE grenades and their damage ticks during deception will get the ambush multiplier (the elemental DOTs they trigger also)… Add the relevant bone and those grenades will have teeth …
There are a LOT of COMs that boost ambush (wiki Killer, Professional, Spy, Survivor, Legendary Killer, and Legendary Ninja class )