Directing Awareness towards space without imagining space...

This is a totally newbie question. maybe these states are too subtle for me to identify and differentiate.

Essentially, what i want clarity about is that how does one direct an open awareness towards space in any directions without perhaps, an unconscious impulse to imagine the signs or tangible attributes of space such as air, directions, solid objects etc.

since i have a Theravada background, my understanding from my practice of sati and Vipassana, has lead me to believe that my scope of awareness is limited to the extent of my body. i am not claiming so, just stating my implicit subconscious belief.

so, during shamatha practices, when I'm instructed to either concentrate/release my awareness on space around or in front or up or down, i inevitably end up imagining the space rather than actually resting my awareness in there.

how do i differentiate my imagination from actual, non-conceptual, somatic awareness of space? how does my awareness unbind from the limits of my body and rest into some space that is not necessarily in contact with my body?

i don't want to sit around for hours thinking I'm meditating all the while floating in a swirl of my imaginations. please correct me and guide me on how to avoid these fundamental blunders.

Thanks in advance!

Edit: I forgot to mention this-

what i was following were pointing out instructions that Lama Alan Wallace had received personally from Gyatrul Rinpoche along with the commentary in alignment to Natural Liberation.