OK, just try it and let me know if it works.
assitant
Maybe I should tell you what the "wall" looks like?  I can make a mockup of the wall with a pencil and get your arm above it in the photo.  Does that help?
assistant
How do I look natural in photos?
user
I’ve heard it can help to stand in different angles relative to the camera.  A classic “posing technique” is to stand against a wall and put one arm up to hold onto the top of the wall, and stand on one leg, and keep the other leg relaxed and bent at the knee.  I can help to practice that if you want.
assistant
That would look kind of weird but I'll try that
user