Cost placeholders by shipping class

Hello.

I’ve playing with the cost placeholders, specifically with the quantity one [qty].

I have a few shipping classes, for each of them I have a price, which includes an extra per item fee using the qty placeholder. So,

Shipping class A, “1 + (0.50 * [qty])”
Shipping class B, “2 + (1 * [qty])”

Case 1)
If I get an order with items of the same shipping class, then everything is fine. i.e 2 items of class A, total price = 1.50 (1 for the first item, 0.5 for the extra item)

Case 2)
If I get an order with items of multiple classes, things get messy. i.e 1 item of class A and 1 of class B, total price = 4.5 (1 for the first item + 0.5 for extra item + 2 for the other item + 1 for extra item )
For this case I would expect the price to be 3

Case 3)
If I get an order with items of multiple classes, things get messy. i.e 2 item of class A and 2 of class B, total price = 7.5 (1 for the first item + 1.5 for 3 extra items + 2 for the other item + 3 for 3 extra items )
For this case I would expect the price to be 5.5

Looks like the extra item fee specified using the qty placeholder is applied for each item in the basket and not for each extra item that belongs to the same shipping class.

Is there a way to achieve applying extra item fees that are calculated only if the item belongs to the same shipping class as another item?

many thanks
Alan

https://wordpress.org/plugins/woocommerce/