Here is an experiment I have found useful for noticing how thoughts create an appearance of extent or space.
Close your eyes, and visualize the room you are in. Notice how any sounds and other sensory inputs are imagined to occur in particular locations within this space. And notice how the experience of space, and of perceptions being located within this space, all comes from imagination, from visual thoughts.
Then open your eyes, and see if you can notice how there is pure perception, and also an overlay of this same image of space, which then helps spread out, organize and locate the various perceptions in different locations in space.
With some practice and exploration, it is possible to experience directly this overlay, and see that it comes only from thoughts.