Answer:
It depends on the sofa. There are some short sofas out there and tall sofa tables. Generally the sofa table is supose to be around top of the sofa. However, now a days sofa tables are not used as much behind the sofa. they are used as hallway tables or just accent tables. They are also called console tables from time to time. My profile will give you the link to my company where there is a large collection of occasional sets you can look at.