Re: One little theory hang-up
I'm slightly confused by your question. If u r playin in c maj then so long as you are playing the notes from c maj you are still playing in cmaj! If the chord stays the same, and you move to say, the "Dorian position" as I'll call it starting at what woul be the 10th fret for ease of explanation, you are still playing c Ionian or c major, not Dorian. If the chord changes under you, the notes you play now have a different function or relationship to the chord, therefore giving a new tonality.
You can play any mode in any position; the aj scale can start from anywhere on the fingerboard not just the 8th fret.