I think it's a matter of development- the RTZ is the first place you go to when you learn to project (for most people) but once they've been in it a few times, they evolve into going 'farther out'. There is a tendency to, when you go out in the astral, to keep going there- it's a habit of the subconscious for various reasons- and I personally have not figured out a way to insure that I go out into my rtz area.
What I have found is that if I RV (instead of exiting) I tend to see my whereabouts, and if I have an OBE I don't stay around much, if at all. Also, if you get out of your room (again, prob. a subconscious thing) 'portals' like doors and windows, & mirrors may shift you to the astral.
I suppose since this is prob. an 'evolution' thing, you should maybe try using affirmations to try to convince your subby to let you stay around longer- but I'd just not fight it and go along, it may be a HS thing, getting you to progress whether you want to or not.
It's hard to say.