The campaign started with them shipwrecking on an unknown island with a massive jungle. They are in a new continent (after years of playing in the same continent) and know nothing. They have been attacked by dinosaurs, giant apes and beastmen berserkers. It is a very heavy and thick jungle area they are in right now. The last encounter was in a clearer area which was what the beastmen used for rituals.
I really don't see how this environment is that conducive to the problems you are citing. Last encounter aside, how exactly are they drawing 150 foot sight lines in a thick jungle?