An underground path would only confuse players, since this layout is not symmetrical. I say just try to clip some of those upper spots, and hint brush loads of places. If you detailed correctly, or if spook did in this case, you should be dropping your numportals by like 2000. Adding in hint brushes wont raise you more then 1000, and Im guessing that you have like a 5000-6000 numportal map without any special brushes, so detailing and hinting will only help. Make sure none of the walls or terrain or necessary vis blockers were detailed though, because that can cause VIS to display large portions of the map. Just clean this map up, less overlapping of brushes and stuff like VIS and your good to go.
-Cusoman