This exactly.
I've tried couple of times with my side project on show HN - https://tardis.dev (aimed at algotraders) and it didn't pick up, but on the other hand on reddit algotrading sub I received useful feedback and even few paying users.
A set of small communities, like on Redit, have a much more predictable behavior. If you have content that interests one of them, it is very likely that it will get picked.