Immediacy is a psychological construct, e.g. defined by Mehrabian (1981) as communicative behaviors which enhance closeness to another 
Social presence is different. Firstly is not being alone, but also being able to provide and read clues required to accomplish a task.
See also: social presence
Links and Bibliography
- Kelley, D. H., & Gorham, J. (1988). Effects of immediacy on recall of information. Communication Education, 37(3), 198–207. https://doi.org/10.1080/03634528809378719