172510's frame of reference is established in this sentence:
You need to see the runway while doing your circuit. At the standard approach path angle of 3°, a 3000m visibility will allow you the see the runway (provided it's a hard surface one) at a 500 ft height. (Basic trigonometry).
The assumption is that the (required) Field of View (FOV) is directly related to the slant range visibility associated with this approach angle (a not unreasonable assumption with large fixed-wing aeroplanes). Within this frame of reference, at 500', nothing can be seen in front of the aeroplane that is closer than 3,000 m.
Of course that is an unsafe assumption because the FOV in helicopters has been improved such that steeper approach angles and flexible departure and arrival angles/profiles are facilitated.
However, there is a serious point within this post and that is that as visibility reduces, it may be necessary to reduce the operating height (sometimes below a safe level) to ensure that visual contact, ahead of the helicopter, can be maintained. This is necessary for two reasons: (1) to ensure that there are sufficient visual cues to maintain control; and, (2) to maintain spacial awareness. Both of these are important for an inexperienced pilot because they improve confidence and assure well-being.
Jim