This is our situation
We will have a base item (gold chain) which has 10 variants (setup as variants and SKUs). Each of those variants will have a different cost price (the variants are different lengths so the cost price increases)
What I want to do is set a special price of cost+%. However, when I do, it's only calculating it against the item base cost and not the individual variant costs. I confirmed this in sandbox testing
SKU Setup
SKU Cost showing
Special Pricing Setup (its incorrectly showing the unit cost as $4 which is what's on the base item), each SKU has a separate cost, 45cm is $2, 50cm is $4, 55cm is $6)