Sion killed large monster didn't +10hp

Sorry i'm not a native speaker, it is hard for me to explain.

But usually in Rank game, i took +9%hp runes and masteries with +3% hp after i bought Stalker's Blade - Cinderhulk. that Sion W kill large monster passive will not be count. Because usually i can get 7000+hp at 2030 mins but right now i only get 5000+hp around 2030mins