Simple percentage off isn't the only type of promotion you can create on Amazon and if you want to experiment, Amzpromoter allows you to do so. 

Step One: Seller Central

Tiered Discounts (Buy 2 Get 30%, Buy 3 Get 50%, etc.):

To create tiered discounts, go to Percentage Off promotion. In the Step 1: Conditions, set the criteria users need to carry out in order to obtain the discount. 

Buyer Purchases: Select how many items costumers need to buy to get a discount
Purchased Items: Product ASIN the promotion applies to
Buyer Gets: Discount amount a costumer gets
Applies to: Purchased or qualifying items

You can also go advanced, where you can create multiple tiers, e.g, Buy 2 Get 15%, Buy 3 Get 30%, Buy 5 Get 50%, etc. 

Buy One Get One:

Go to Advertising -> Create a Promotion and choose Buy One Get One.

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