LOS Question from Hill

[saracv3]

Also related to the above question: if trees and towns are 20 meters high, what is their effect on LOS from a higher elevation hill that might be, say, 40 meters or higher. In Crete, there are several hills that are 60 meters or higher with very defined downslopes dropping 20 meters every 1-2 hexes. Yet light forest is all through out these slopes. (Olive trees, actually.) What is the blockage to LOS here?