For observation is better an island like 2nd or 5th, less damage more hits, less times you need to do reset, closest to gun or slingshot npcs location from spawn.
Level the mastery up, each 100 mastery levels your haki would grow more and more further up your body, remember it’s the armement haki, not the observation
Sitting in game finding them, sadly I’ve only got one legendary but today ima be posting 2 more fruit showcases, which are the ones I already have recorded until I get some more fruits