EntityVisible/Line Of Sight

So I was looking Fredborg's line of sight code(http://www.blitzbasic.com/codearcs/codearcs.php?code=532) Its a great peice of code. However it seems that it can only check things that are in a direct line infront of it. In his example I changed the height of the wall entity to .1 and the "player" could still not see over it. What could I do to make it so the object sees in a 3d cone of vision instead of the current 2d cone?

..I think visibility is define by pivot point of each entity, so, if your wall pivot point is out of viewer range, it will not be visible...