They have his Bird Rights so they can pay him whatever they want up to the max. The only problem is that there's no use of paying him anything if you are getting bad JR. It would be nice if they could convince him to pull a Duncan and be happy to take less to be with a winner. That's why I think a 4/6/8 contract with the last year being a team option is good. He gets at least 10 guaranteed and 18 if he plays like he did with the Cavs last year. Looking back opting out was pretty dumb. If he had opt'd in and played like he did last year he would be in line for a raise.
Now that they signed RJ it makes JR even less necessary. If they give him 4 mil it will basically be paying 18 for him once the tax is paid. A backup unit of Mo, Delly, RJ, TT, and Andy isn't bad even with Jones and Miller(can't be worse than last year) still on the bench. JR makes them better I don't think they will regret letting him walk if it doesn't work out.