Hopefully your new Referral Program Rules will be a system that everyone can take part in and not just the first signups. You would be  shooting yourself in the foot only giving rewards to your first affiliates.

You won't get any new affiliates, which equal less sign ups.

A teared system for all is the fair way to go or a straight percent per sign up. I think the 2 month deposit needs to be extended to. If a sign up through an affiliate makes a deposit 3 - 6 - 12 months down the road that affiliate still brought that sign up to your exchange and they deserve credit for doing so.