Adding price percentage based on other options

We are using product options to allow customers to select size and material type (among others).

I see there's an option to add a percentage to main product price, but this isn't suitable or desirable in our instance.
Some materials are more costly, so we'd like to add a percentage based on the size (another variant / characteristic) applied to the product.

Is this possible, or is there another way to accomplish without custom code to determine price?

That's not possible.
If you want to recalculate the price dynamically like you're saying, you would need to develop a quantity price recalculation plugin as explained in our developer documentation.