Yes I am aware of that thanks, but my experience is that buyers graze,
looking and buying as they go, and not noticing it is the same seller.
Also if I have something similar to a new order I often contact the
buyer drawing their attention to it and offering free postage if ordered
at the same time. It is a powerful selling tool that SD has taken away.
The only way out of it is to cancel all the orders, and then ask the
customer to re-order in on go.

The basic fact is that it is not possible to determine postage needs
until the buyer has completed all their purachases, and expressed any
special delivery needs.