When legal departments have six or fewer lawyers, not counting the general counsel, it is my impression that the predominant structure is flat. More often than not at that number, all the lawyers report directly to the general counsel. By “report,” I mean the general counsel sometimes assigns them work, evaluates their performance, and expects to be consulted with fair regularity and certainly on important decisions.
Above a half dozen lawyers in a department, one of the direct reports may have his or her own reports. I consider that the third level of lawyers: general counsel, direct reports to the GC, and third level reports to one or more of those direct reports. There may be empirical findings on this tipping point for reports, but I am not aware of it.