it’s a one item increase per boss, you defeat. REGARDLESS of being a dungeon or a raid. possibly scenario too.
In dungeon, it’s decent(From 2 to 3)(33% increase item rate), but in raid… it’s terrible.(from 6 to 7)(13% increase item rate)
at least, you have (possibly) 2 chance at mount boss.(mount seem to be a separated roll, from what i heard, but don’t quote me on that)
According to this youtube video: https://www.youtube.com/watch?v=0ytBafWrFKw&t=243s