There's a few of us coupe owners that have had the same problem.
Mine was about 1" circle of corrosion (bubbling under the paintwork) that was corrected without argument.
I've seen others on here where almost all of one side has been corroded.
Not heard of any issues with bodywork warranty claims on it.
Has it got a BMW history, and has it had any paintwork outside of the network (part of the inspection is a bodywork check)?