Under the rules on Page 109 of TW, Page 32 of BMM, Quoted below:
Partial Cover: Partial cover only applies to standing ’Mechs. Add a +1 terrain modifier to the to-hit number if the target ’Mech is partially concealed (see Line of Sight, p. 99). When a ’Mech receives the partial cover modifier, resolve damage using the standard ’Mech Hit Location Table, but any hits against the target’s legs strike the intervening terrain. Remember that an attacker firing downhill negates its target’s partial cover (see Partial Cover, p. 102).
So, in the First Example Diagram below, the Awesome is firing on the Assassin getting partial cover from the building in front of it. Any attacks that hit the Assassin's Legs hits the building instead.
However in Example picture 2, the same scenario applies, but if the shot hit's the Assassin's legs where does the Awesome's shots hit? The level 1 hill, or the Level 1 Building?
This is a weird corner case as both the Building and the Hill are the intervening terrain, but technically only the Building is granting the Partial Cover. This gets further sticky as the scenario we were playing last night involved one side trying to destroy the Buildings, and the defending side placed all the Level 1 buildings behind hills to prevent LoS to the buildings as per INTERVENING TERRAIN rules on Page 100 of TW/Page 22 of BMM.
Obviously, the Defending players argued the Hill/Building were one piece of intervening terrain, while the attacking side argued that only the hex immediately in front of the Mech counted as intervening terrain.