External Cup headset

I have a 2016 Salsa Fargo with the oem steel fork, and I'm going to change out the fork with a Niner carbon fork.  The oem fork is 483mm axle to crown, and the Niner fork is 470mm.  If I change the lower headset from a zero stack to an external cup (cane creek 40), that should add 12mm to the stack height, effectively changing my Niner fork to a 482mm axle to crown (470mm fork plus 12mm for external cup).  Am I looking at this correctly?

Thanks in advance.

DaveH

For anyone that might run into a similar question, I was able to change the lower headset to a external cup to add to the axle-crown distance.  The original headset had a 4mm stack, and the new external cup has 12mm stack, so I actually only gained 8mm, but that was close enough IMO.  It turned out well.