Minion Rare %

I was looking at my minion details last night and I noticed that there is a line in there that says something along the lines of: When this minion gets the kill, there is 88% rarity of loot.

Does anyone know what this means? Is it +88% on top of my base modifier? Is it 88% of what my normal modifier is? Is it a flat 88% no matter what mine is?