I think that you are saying that if 1 or more posters must be flat, then you send all of them flat. So you end up having "rolled" rates and "flat" rates in an all or nothing condition where if 1 is flat they are all mailed flat. Is that correct?
OR do you still roll as many as you can and then have a separate charge for the ones that are flat? How many flat can be bundled in a single shipment? I still don't quite get it.