what you see is not what you get, Illusions in combat Options

[Brazila]

I am playing a mage in our game and plan on doing something kind of new with some illusions. I am going to quicken an invisibility to myself and then put a trid phantasm in a sustaining focus. That way I can still appear to be there when it is helpful to me. I was wondering how this would work during combat.

Assuming people don't resist either spell, then they will see the form of me that I control with my phantasm. So if I misplace this compared to my true location, they would be firing at nothing. This also got me to thinking about invisibility. What would the chance be of getting hit by random fire? And if there was a spellcaster there, but not astrally active, then would his spells be able to hit me, since he didn't have a true LOS?