What seems to go wrong: It seems in the current situation the "Maximum Qty Discount is Applied to" applies to the order line instead of the total qty in the cart.
What I think that should happen: The "Maximum Qty Discount is Applied to" should use the total qty in the cart and if it is greater than "Maximum Qty Discount is Applied to" it shouldn't apply the rule.
What am I trying to achieve: It happens more than once that a customer buys something and something goes wrong, they want to give them, say 10% discount on the next product (not the whole order, just one product). Giving a fixed amount discount doesn't do it because there are different product prices, etc.
I haven't set up any special rules for the conditions (always applies) I've just created a coupon code to apply the rule. Also it can match any product in the order, but preferably only the lowest.