What's the smallest sprocket size that will fit on an Alfine?

I know that the Alfine sprockets only go down to 18 tooth, but as it’s a standard hub gear fitting you can use Sturmey Archer sprockets, which are available down to 12 tooth.
However, I am pretty sure that if you put a 12 tooth sprocket on an Alfine the chain would foul the hub and maybe also the shift mechanism.
So, what’s the smallest sprocket size that can be used successfully?

I have a nexus 16 on mine

Thanks for the reply. I had a 15 tooth in mind – do you think it would fit ok?