Production Time + Shipping is Lead Time - best practice

we are purchasing our needed materials in Asia and Europe. For Europe and local suppliers it is more easy - there is mostly a short delivery time and 14-30days net payment.

For Asia it is much more complex: mostly 30/70% or 100% in advance. Then production time + shipping time (depending on way of shipping: sea, train, truck, air). It would be great to differentiate between the different ways of shipping and not have one fixed leadtime per item.

The most critical issue: If I add now the “real” lead time the PO contains the due date far in the future. But the supplier needs due date for EXW.

Is there somebody who is handling the topic in a proper way and like to share?

Kind regards!