For special attacks (such as stomps) and items that affect models in base contact, a model fighting in a building is assumed to be in base contact with one enemy model nominated by the enemy player unless fighting in a challenge.
Source: Warhammer Armies Project
For special attacks (such as stomps) and items that affect models in base contact, a model fighting in a building is assumed to be in base contact with one enemy model nominated by the enemy player unless fighting in a challenge.