So it seems that Legendary items are considered Unique items by the game. I have been trying to figure out why Legendary items have been dropping with my mod separate from bosses. This thought didnt really occur to me until I tried to change the item overlay for Legendary items. It didnt work. What ever color I changed the Unique item overlay too, the Legendary would change with it.

I then cranked up the global drop settings for Unique items and Legendary items were dropping about as often as Unique items. Currently my Legendary items have the same spawning rarity as Unique's which means the drop rate is the same for both. So I will be changing the spawning rarity for Legendary items so they do not drop as often as they currently are. Legendary items are not dropping as I intended with this mod.