Per Item - charge shipping for each item individually
This calculation method finds all the shippable products in the cart. Then it finds appropriate locker size for each product and looks up the shipping price for it.
Now the plugin sums up all the found shipping prices and then the final sum is the shipping cost displayed to the customer.
If the customer order two units of the same product (same SKU) then it is considered as two separete shippable items.
Combination with "Amount of free boxes per each paid box"
This calculation method finds all the shippable products in the cart.
Then the products in the cart are split into chunks with size <Amount of free boxes per each paid box> + 1
For each chunk the largest product is found and shipping price of the matching locker is applied.
Finally shipping prices of all chunks are summed up and the final sum is the shipping cost displayed to the customer.
Example: Customer orders 8 products, that fit in the locker as follows: S, XS, XS, M, L, XS, XS, XS
"Amount of free boxes per each paid box" is 4
Resulting chunk size is 5 (because 1 [paid box] + 4 [fee boxes] = 5 total boxes)
First chunk contains products with following locker sizes: S, XS, XS, M, L where the largest locker size is L
Second chunk contains products with followin locker sizes: XS, XS, XS where the largest locker size is XS
Final shipping cost to the customer is the sum of L + XS locker size shipping prices