“A writer,” said Thomas Mann, “is someone for whom writing is more difficult than it is for other people.” More difficult, because there is more for you to do, more that you know how to do, and because you hold yourself to higher standards.
Once you have hypotheses for who is successful and why they are successful, you can hypothesize possible adjacent users segments. This will involve changing one or more of the vectors that you identified.
To understand your adjacent users, it is helpful to understand the attributes of who is successful today and why they are successful. The reason this is helpful is that your adjacent user is different on one or more of these attributes (but not all). These attributes create vectors of expansion.