Apply percentage coupon to entire order (Commerce)
Price calculation in Drupal Commerce always happens at a line item level. There are order level coupons for knocking a set amount off an order total, but we treat percentage coupons as these line item level price calculations. You should be able to adjust the weight of your product pricing rules so your rule that updates the price gets evaluated prior to the rule that applies the percentage coupon to the item. Give that a shot and leave me a comment if it doesn't work.