We all know about power positions in meetings, head of the table, back to the window, etc., but you can also consider how much space people try to occupy. Next time you are waiting for a busy meeting to commence, look around the room to see how the other people attending have marked out their territory. Those who are feeling powerful, or wish to appear that way, will take up as much room at the table as they can. Papers will be arranged, folders spread, and mobiles, tablets, etc., arranged to consume as much of the available space as they think they can get away with.
People who are feeling out of their depth, lacking in confidence or, frankly, in awe of the assembled powers, will tend to reduce their exposure, give ground to others and hope for the best. Their position is likely to be further eroded by the powerful people taking up position within the territory they have marked out, demonstrating physically that they are ready and willing to take on any challenges.
Of course, as with body language, these are general clues that could help you to understand more about what is going on in the minds of those you may wish to influence. Now, do some people watching at your next meeting and see what happens.