Set one margin over what each variant actually costs you at its provider. Costs differ per size, so a flat retail price is a different margin on every row — and at the wide end it can be a loss while the average still looks healthy.
The steps
POD — reprice a product runs source → priced → table → approve_reprice → apply.
Who can run it
POD — reprice a product reaches an instance's own resources, so it runs on an operator's Leumas Studio; open it here to read and adapt it.