Dodge, the place where I was careful of the green zone had few landmarks and the (edit) edge of the zone was not logical. It started on the tip of a point (not sure exactly what part of the tip?) and then it see-sawed up the coast for about 8 km or so.
According to Google Earth where I mapped the long and lat given with the green zone map, so I could see the corridor along the coast, it varied between 500 m and 250 m, give or take 100 m

.
So, I got some basic line-of-sight references, but when I was enthusiastically paddling all over the place and even when I was trolling two lines and trying to turn around by doing a very big circle to avoid a cross over (failed) then I had no idea if I was in or out

(Out of the green zone I mean, not the yak. If I was out of the yak I would have noticed probably when I made a beach landing and tried to hop out.)
So, I reckon sightings can be very useful, but some of those zones are like crab marks on the beach.