Hub can define an entreprise fee on products/orders based on total weight of the order [WIP]

We have a need that has been reported by a “wholesaler” type of users.
Those users seem important to me strategically as they carry on huge volumes of sales so can be active users and contributors to the commons.

This hub buy products from various producers in Spain and organize sales and deliveries to retail shops in France on a national level. When she organizes the logistics, when huge volumes are bought, the price for transport is digressive. Price will also depend on delivery zones (that could be managed through various shipping options eventually). She needs to be able to setup a fee on orders/products based on the total weight of the order.

There are two ways to express the need (waiting for user feedback to clarify)
1- Charge a variable amount per order based on total weight of order
If sum of (weight per item x nb of item ordered) < 250 kg, commission is X€, if between 250 and 500, X€, etc.). Fee corresponding is added to the whole order at checkout, not included in product price.
2- Charge a variable % per product based on total weight of order
Same calculation rule BUT here fee is applied at product level, so the ideas is that by default when open the shop, products include % for total order below min threshold. When customer add a product that makes the total weight of the order go beyond threshold, all prices are automatically recalculated and dynamically change in the shop to reflect the new price (probably with some nice pop-in: your total order is more than Xkg, you now get a reduced price!)

From previous discussion it seems that the user doesn’t want the transport fee to be added at checkout time as she experiences a high “drop order rate” when she does so, much higher than when she includes the transport at product price and display a discount if some threshold is reached. But I asked confirmation to understand clearly the need, will precise when get answer.