Import combinations: Impact on the Price from CSV with taxes included

[Aldeag]

Hi, I have a doubt. 

I am importing items with combinations (footwear) by CSV. Some sizes have a different price, so instead of putting a price on the item (product) and the impact on the combination, I am putting the price of the product "0" and in the impact I put the final price. With which I avoid having to calculate what is the price difference to add in the impact. I don't know if this is the right thing to do it.

The problem is that if I import the price from Product, I can choose Tax excluded or Tax included

But if I import the price from Combinations, "Impact in price" appears but it does not indicate whether or not it includes the tax. And it does not.

The fact is that I indicate in Combinations "Impact on price" and the final result is that VAT is added to a price that already includes VAT, that is, twice.

How do I import so that the final price is the one I want, including VAT, without having to calculate the price without VAT inversely? (Dividing by 1.21 as my VAT is 21%) Do I have to change something in the "core" of Prestashop?

[Aldeag]

Long ago and still no answer?
No one has the same problem?

Please.