I think mana and life leech are worst on exori mas, same logic as gfb/avalanche... while the exori min might work similar to exori/exori gran
You should try to lure the monster in a way to make a line of tree to use exori min + exori + exori gran, I didn't used much the exori mas, only when I had a lot of monsters on the screen, especially low life ones (like a lot of sandscrawlers)