The only time I've experienced what you describe is during sleep paralysis. I've seen people appear next to my bed, looking down, with me being unable to move. It may sound cowardly but I keep my eyes shut a lot during sleep paralysis, it's just that if I see what's there I can't ignore it and I become fixated. I've seen all sorts of things when waking up, sometimes people standing in my doorway and I can focus on them for a good few seconds, just long enough before I realize that I ought to be shocked. Other times, stranger things such as symbols and the like.
Regarding encounters of your kind, I don't know enough to say anything worth taking seriously. I have had experiences when people got too close to my personal space but my focus is usually on making sure I don't get too nervous. I don't want to distort things out of fear and create a regrettable scenario. I did meet someone who appeared to be afraid of me while I was 'out', I just slowly backed away with my arms apart in order to communicate that I wasn't there to cause trouble for her. I have had a sexual encounter with someone who looked like one of my friends from a few years back, what looked to be a lifeless body suddenly became animated and grabbed my hand so that I couldn't move and began kissing me.
These are some of the more confusing moments, I don't know what to say. I am suspicious of anything that assumes the guise of a person I know without communicating from a 'distance' first.
Creating scenarios in the astral doesn't always go smoothly. A lot of it depends on how excited you get I find, but most of it has to do with preparation beforehand (although this comes closer to phasing). I've stayed in the same area for what seems like a good few minutes without being able to manifest anything at times. Lucid dreams and false awakenings also present some problems for me as the only thing I tend to care about is creating scenarios. Obviously I'm missing the point and there's something else to be done/experienced in that environment. My most direct manifestation came during sleep paralysis, it took about one second to start but I only attempted to create an auditory phenomena of some kind (in this example 'alien sounds', purposely to scare myself). The biggest grin swept over my face when I realised it came in answer to my request. Had I not been prepared I would have been very upset.
I haven't had much luck getting to the 'sandbox' environment, or rather, when I'm there it's never for long but the experiences are incredible. I specifically try to avoid involving/imagining other people as I'm more than happy to be alone in those situations. So much to experiment with/express with etc... Creating new bodies for myself is where it's at

Robert Bruce seems to insist that firmly stating a command will do the trick. It's something I should keep trying I feel.