I've not played with the SNG's, but have you found this link yet?
He's modified that exact version. Lots of folks have found some great info there. That's the first one I found as well.
I don't think you can have too many holes in the firepan, but you just have to make sure you can still close them off for control. In the link above, he's added a damper sort of like mine over all the holes he has in the pan.