I would say that's not totally true. The judge and/or jury needs to place themselves--as best they can--into the mind and position of the person on trial. They have to think of what that person reasonably believed, not what they reasonably believe.
I took what RJ was saying as the trier of fact and the accused having an equal footing in it, but from the way the statue is written I don't think they do.
I agree that the thought process is to put yourself in the shoes of the accused, but then you (the judge or jury) are going to decide if it is reasonable to be in fear of serious injury or death while in that predicament. They aren't "in the mind" of the defendant, they are in his predicament.
Under FL law, it isn't that the objective reasonableness (that's you agreeing it's appropriate to be in such fear, in that predicament) and subjective reasonableness (that's Zimmerman saying he was in such fear) are on equal footing. The law is that BOTH elements must be present, in order to justify the use of force in self defense.