There's nothing actually wrong here. The sector effect in question triggers star posts in the same sector, and the sloped part is a different sector. As for getting it to work as you intend, I don't know (without placing another star post, which would be annoying to have to do). The only thing I could suggest would be to try making an intangible invisible FOF that covers both sectors from the top to the bottom, give that FOF the sector special thing, tag the FOF onto both sectors, and see if that will actually do anything with the star post.