Our bracket rocks on a nest drawn with five contacts

I'm holding the tooling order for an FR10 bracket-loading nest. Some milled brackets sit firmly in the bench sample, others rock until clamped. The drawing makes all five contacts look equally important. Supplier suggests a stronger clamp. I reckon we need to understand which faces actually locate the part first. But I don't want to tell the toolmaker to remove a support that has a good reason to be there. What would you ask them to demonstrate?