Use separate discount codes per SKU tier (one campaign per tier)

Create one Advanced Discount Code campaign per SKU tier, each using a Product Discount module targeting the appropriate SKUs/variants and the desired percentage or fixed discount. Generate and send the corresponding code(s) to customers via Mailchimp (e.g., CODE-A for 'A' SKUs, CODE-C for 'C' SKUs). If you must use a single code, the supported alternative is to apply a single product discount value to all targeted SKUs (i.e., same discount across selected products), which does not meet the requested per-SKU tiering.