How do I avoid this problem in the future?

I have just started using the IM prep center. I submitted my prep form expecting to be able to add the tracking numbers once I received them since this has been my experience with other prep centers. I discovered that I couldn’t. Then Blain’s Farm and Fleet sent all but ONE unit of my product under one tracking number and sent the remaining unit later on another tracking number. The prep center sent the first batch to Amazon. Then the straggler was sent in by itself. This resulted in a ridiculous shipping charge for the last item compared to the other units.

This was a BOLO deal. When ordering from an online retailer we can’t control how many shipments they break the order up into. How do I avoid wracking up high shipping costs on stragglers? If I had waited to enter the prep form until I had all tracking numbers (again, didn’t know I couldn’t add them later) or deleted the first prep form and created a new one with tracking numbers, would prep have waited for the additional unit or would they still have sent this in two shipments?