Nitro Issues

So this is my first attempt at pouring my coconut milk stout on my new (used) nitro set up.  My pours have too much head and it takes a lot longer for the cascade effect to finish.  I think I may have over carbed the beer before I put it on nitro.  Please take a look at my method and suggest how I should change my method and fix the issue I have now.

1.  Racked beer to keg and set keg on 12psi @ 40 degrees for 3 1/2 days. 
2.  Connected keg to nitro (75/25 beer gas) @ 32 psi.

I tried a couple of different settings on nitro, 25 and 30 psi, but it still comes out w/ too much head and cascades too slow.

Thanks!

I try to carbonate by beers to about 1.5 volumes first, you can adjust to taste from there.  (use a carbonation calculator on the internet or in brewing software if you use it.) 12 psi at 40 deg will give you about 2.5 volumes. Other than that you got it!

Thanks.  I de-carbed the keg and put it back on C02 @ 6psi, so we’ll so how it turns out.