[Diaspora] My other 2 Rules Questions

[C. W. Marshall]

Exactly. Setting up an ambush does become increasingly expensive for  
the attacker, and is only worth while (in the fate point economy)  
some of the time -- not every attacker can capitalize on every  
opportunity. The only thing you can't do is compel an opponent not to  
move based on one of your own aspects... it has to be something in  
their control (which, through maneuvers, includes the aspects on the  
zone they are in!). Similarly, you can't compel based on the aspects  
of a zone that the defender isn't in.

Hope this helps.