Problems calculating shipping when there are a mix of local and aliexpress items

Hello,
I have a shop where I sell items made by me (local items) and also the items coming from Aliexpress. If a client select both local items and some coming from Aliexpress, the shipping rate is calculated by this formula = Flat rate + Aliexpress Shipping rates using the option “Calculate Aliexpress shipping cost of all items in cart and add the cost to all currently available shipping option” at Frontend Shipping options, so far so good. However, if I use that method for calculating shipping and the client selects just aliexpress items, the shipping price keeps calculating by the same formula = Flat rate + Aliexpress Shipping rates, which causes the total shipping rate to increase a lot, since there’s no need to add the flat rate.

In the case that a client select both local and Ali items and using the other options to calculate shipping like “Do not calculate item shippings, only save customer’s shipping option” or “Create a new shipping method and make it the only available shipping option” will cause that during checkout the client will have the opportunity to select the cheapest shipping rate, which might not be enough to cover both kind of items.

What I’m requesting is that there should be a way to calculate the correct shipping whenever the client selects either local, aliexpress or both items, maybe using an specific shipping class for local items, so if there are not items with that specific shipping class in the cart, avoid adding the flat rate.