Create a percentage discount coupon with a maximum value
If you're using the latest version of Commerce Discount and Commerce Coupon, you can accomplish this with just two rules connected to a single coupon code.


Create a Coupon Code by going to Admin→Store→Coupons->Create Coupon Code. Save it.
Create a new Discount (Admin→Store->Discounts->Create). Set it to Order Discount and add a Total amount condition. Set the condition to less than and the amount to 2000. Set the percentage discount as you desire. Finally, add the coupon code from step 1 to this discount and save it.
Create a another Discount. Set it to Order Discount and add a Total amount condition. Set the condition to greater than or equal to and the amount to 2000. Set the flat discount as you desire. Finally, add the coupon code from step 1 to this discount and save it.


Now, when a customer checks out, the coupon will attempt to apply both discounts, but because of the condition, only one will apply: $200 if the order is $2000 or over, and 10% if the order is $1999.99 and under.