How can I get Flow to assign the cheapest shipping method?

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I use Flow to setup my shipping labels. I ship records so can use media mail. That's usually the cheapest option but not in all cases. When shipping packages over certain weights to nearby locations (Zone 1-3 I think) it can often be cheaper to use Priority Mail. Is there a way to have Flow deal with this directly by assigning the cheapest allowed shipping method? Right now flow is assigning a more expensive (and slower) shipping method which my warehouse team are then blindly printing without realising there are cheaper options.

My spaghetti shipping flow