In the galactic overview, clicking anywhere within the star system's rings (the double circles around each star which are also connected to the star lanes) should bring up the system overview. As of this post you currently have to click on the star itself most of the time. Maybe widen the detection area?

Although I like the idea of wider clickable are, it could mostly go to the inner ring around the star system as it would collide with orbitting fleets otherwise. But if it is possible to enlarge the click area, I'd like to have this