No need for me to reiterate the math side of theoretical positioning, and that is really all it is good for, theory & written tests (unless you have a ruler affixed to your aerial). Practice & experience is still the best method, in reality try to establish landmarks on the aerial as it extends, as to how far out it is. In some cases I've seen departments that paint small alignment marks indicating how far out the ladder is. I always keep 2 9"-12" broom stick handles on our platform with a couple of bungi cords apiece. I affix these to the base of the platform on each corner with about 6-9" sticking out from the paltform. As I maneuver in towards the building I can see when the stick touches the building and I know I'm 6-9" away. This way I don't have to "sneak up" on the building and it causes no damage to either the platform or the building.
As for the best way to approach a victim for rescue, each has it's own merits and arguments. The victim will try to jump down & in, the victim will try to jump up & grab. Situation will probably dictate what tactic you should use. As Pascal stated I have found that either rotaing or extending in, top rail of platform slightly below victim level works best for me. If they do try to jump, it offers the least chance for miss/injury by the victim.
I know that this is probably outdated and doesn't really answer your question but your question has too many questions attached to it as you are aware. Drew hit the nail on the head though. As a legitimate test question it has to have a reference and the reference needs to give you the information you need to determine the answer. Hopefully your department has resolved this by now and that the above information helps in the reality of your aerial operations.