Affiliate plugin is recurring with Pro Sites?

This is just a simple question. I've installed your Pro Sites plugin and the Affiliate plugin. I want to offer my users a portion of any Pro memberships they refer. example. A user refers a $20/month pro membership and receives $5/month in return.

So the question is - is that how the Affiliate plugin would work in this case? Or would it be only a one-time payment of $5 to the user?

Thanks,

Ray