Variable Product with different shipping classes not working

I have enabled flat rate shipping, and a product with the base shipping price at 0.00 (maybe this is wrong?)
I have set up the 2 variations for the product, each with their own shipping class and prices (7.85 & 5.50)
But no matter what I try, the flat rate says “Flat Rate (Free)” even though the product variable is 5.50 or 7.95, I’m assuming because the base price is 0..but how do I get the variation shipping classes to work? what am I missing?

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