Strange how MOS139 specifies this (among other things) for a CA/GRO:
14.2.3.4 A permanent CA/GRS must be provided with the following facilities and documentation:
(a) a suitable work area that provides the operator with a full view of the manoeuvring area and circuit area;
yet many an FSU providing a local AFIS or centre providing an AFIS to a remote AFIZ did not have to, and most local ones didn't.
(I believe there was a perception amongst the ATC-dominated heirarchy of the old Departments that an FSO who could see the runway, circuit etc might start to "control" the movements).