The basic idea is that the space around your body to the maximum distance reachable by your arms/legs called "peripersonal space" (https://en.wikipedia.org/wiki/Michael_Graziano#Peripersonal_...) is integrated into a larger body schema maintained (partially) in the somatotopic map and its homunculi. Proprioception is part but not whole of it and how it might be regulated by higher executive functions like focus/attention is AFAIK not clear.