He’s behind you!
Oh no he isn’t!
Oh yes he is!
Sound like a Christmas panto? Sadly it’s Dungeon Saga.
Q: When is a model behind another?
A: When all the squares covered by its base are in the area marked behind in this diagram. In other words, the model must be entirely behind the red line. The red line in question is a continuation of the line dividing the front and rear arcs of the target model, in this case a Hero facing the top of the page.
If any of the squares a model covers are in the area marked in front then it counts as being in front of the target.