from the product page(matrixgames):
Line of Sight calculations use a 3D technique -- ray casting on the map geometry -- instead of the rules in the book. This allows the computer game to have more complicated hills than in the board game.
here's the link to the product page incl. more exceptions/differences boardgame/pc game version:
there's an ingame LOS tool - use 'L' keyboard shortcut from any hex to check LOS.
unfortunately not documented in the pc game manual.
here's a link to all hotkeys: