According to BattleTech Rules:
Intervening Terrain
Terrain along the LOS between the attacker and the target that actually lies within the LOS (not including the hexes occupied by the attacker and target) is called intervening terrain. Intervening terrain has the following effects on LOS:
Light Woods
Three or more hexes of intervening light woods block LOS. One hex of intervening light woods combined with one or more hexes of intervening heavy woods also block LOS.
Heavy Woods
Two or more hexes of intervening heavy woods block LOS. One hex of intervening heavy woods combined with one or more hexes of intervening light woods also block LOS.
Terrain Modifiers
Terrain can affect the probability of a successful shot by forcing the attacker to account for intervening land features. Special terran modifiers appear below:
Light Woods
Add a +1 terrain modifier if the target occupies a light woods hex. In addition, modify the to-hit number by +1 per hex of light woods intervening between the attacker and the target.
Heavy Woods
Add a +2 terrain modifier if the target occupies a heavy woods hex. In addition, modify the to-hit number by +2 per hex of heavy woods intervening between the attacker and its target.
Edited by Maverick01, 10 July 2012 - 06:22 PM.