Nirvana Major Id

So I know that nirvana has a major id that allows for spells to have a 50% chance to not use mana however I would like to know how exactly this works in game when spamming. If you say have a two mana spin when you spam the mana cost is 2-2-3-4-5-6 ect for each spin. so with nirvana does the free spell work into the mix like
2-(free)-2-3-(free)-4-5
or like
2-(free)-3-(free)-5
if you understand what I am saying. Currently considering getting one and want to know this so I can accurately estimate dps.