If you are looking to have goal targets that show a measurable decrease, there are two ways you can set up your key results to do so.
The first way would be to use a numerical metric in which the starting number is higher than the target number. The system would then see that a lower number is going to be closer to the target number and provide you with progress/results that represent that. For example, you can have a goal where the objective is to improve the customer experience. You would then make a key result measuring the decrease in customer tickets from 2 to 1 with a numerical metric. The platform would understand that this decrease is the progress you would like to see. Therefore any number between 2 and 1 that is input would still show an increase in progress.
Similarly, you can use the metric percentage to measure the percentage decrease in customer tickets. Therefore, if you had a key results where the goal was to decrease the customer tickets by 50%, you would set the metric as a percentage, the starting number at 0, and the target number at 50. Therefore measuring the percentile changes in customer tickets, but still at a reducing rate.