There are a few rules in the game that are a bit ambiguous or have gaps; these are my rulings on how they work.

The Illusion talent has no maximum range, but requires line of sight. Illusions that leave your line of sight remain in existence, but cannot be concentrated on (see below). Note that the Illusion Bond talent grants you line of sight to a humanoid illusion at all times after it is made, making it a potent scouting tool.

Illusions can only actively respond to their environment if you are concentrating on them as a Standard action; otherwise, they remain relatively static (though not perfectly motionless - an illusion of a person will still shift and breathe, an illusion of a blinking light will still blink, etc.).

If you are concentrating on an illusion that is attacked, it can attempt to dodge; its Reflex defense is equal to 10 + half your heroic level + your Charisma modifier; larger or smaller illusions also take the appropriate size penalty or gain the appropriate size bonus. Illusions have no Fortitude or Will defense, and opponents who target either are always considered to have "hit," and thus learn the true nature of the illusions.