The below is right from the documentation which you can find in your download in user_guide.html file
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Value Definition: this field is used instead of the value field if you want to create progressive coupons. Progressive coupons are coupons that are based on the number of products customers buy. For example, you could have a progressive coupon that says if a customer buys 1 item, then give him/her a 10% discount. But if the customer buys 2 items then give him/her a 20% discount... etc etc. The input field is very specific. Using the example just mentioned, the input would look like 1-10;2-20;. As a definition this can be broken down to [quantity]-[value];[quantity]-[value];...etc etc.
By default the product count is done on all products selected. For example if you have products A, B, and C, then 2 A's are treated the same as 1 A and 1 B, in terms of the count. By clicking the checkbox 'Apply Distinct Count', then 2 A's are treated as 1 product while 1 A and 1 B are treated as 2 products.
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I do not believe this would solve your problem. If you want to give a definite discount then set the coupon discount to an amount instead of a percentage.
