Is there a word that could be used in an instance where you want to indicate that a lower number is better than a positive number?
In golf, scores are _______. to indicate that a low score is a positive thing.
Seems to me the concept of inverse proportionality (IP) needs to be part of an answer to your question.
At its simplest (which is what I'm comfortable with), inverse proportionality is the phenomenon in which one variable goes up in value while another related variable goes down.
If, for instance, you are a cold-weather lover, your enjoyment level is at its highest when the temperature is at its lowest. The two variables are in inverse proportion to one another. Notice how the IP thing doesn't work with the hot-weather lover, because their enjoyment level goes down as the temp goes down, and up when the temp goes up. I guess one of the terms or phrases for the latter is in direct proportion. (Mathematicians, feel free to correct me!)
In golf, as the numeric value of your score goes up, your perceived competence level as a golfer goes down (unless you are really trying to let someone beat you!), so the two variables (viz., competence and score) are in inverse proportion to each other.
An amusing way of looking at the IP phenomenon is as follows:
The chances of a buttered slice of bread falling onto the carpet, butter-side down, is in inverse proportion to the value of the carpet.
While I agree that the concept is referring to @rhetorician's answer, inverse proportionality is usually used in mathematical contexts and sounds strange to me otherwise, because then you have to say something like "winning/happiness/success/...? is inversely proportional to your score".
Really I would just restructure the sentence: "lower scores are better in golf". In the amount of reading I have done in the health space, where cholesterol and blood pressure are spoken of in the same fashion, I've never seen a synonym for this phrase.