As far as I can see there is nothing wrong or inadequate in your original reps, (Hippocrates said "good stuff"). However, the regulations for traffic signs have been studied in more detail since cases of very high, (even absurdly high) have arisen, and recommendations on traffic sign positioning are found in Sectio 5.1 of the Traffic Signs Manual 2018: -
5.4 Mounting heights
5.4.1. Signs should be mounted such that the lower edge of the sign is generally between 900 mm and 1500 mm above the highest point of the adjacent carriageway. Signs mounted at the lower end of this range benefit from receiving the most illumination from vehicle headlamps, but they are also prone to soiling due to spray from passing vehicles. Mounting heights at the higher end of the range should be used where this or obscuration by other vehicles is likely to be a problem. Speed limit signs and other safety-critical signs will not normally be mounted lower than 1500 mm above the carriageway.
5.4.2. Where signs are erected above footways and cycle tracks, adequate clearance must be allowed for pedestrians, cyclists and equestrians. Interim Advice Note 195/16 ‘Cycle Traffic and the Strategic Road Network’ requires a minimum height for such structures of 2300 mm for pedestrians and 2400 mm for cyclists. However, to minimise the environmental impact of signs, particularly large directional signs, consideration should be given to adopting lower mounting heights. A minimum clearance of 2100 mm should be maintained over footways, 2300 mm over cycle tracks or shared-use facilities and 2700 mm over equestrian routes.
5.4.3. Detailed consideration may be necessary for the combined effects of location and mounting height at some junctions in order to take account of the differing eye heights of drivers of cars, lorries and other road users. The aim is to optimise the benefits and minimise the disadvantages to any one category of road user at a given site. Alternatively, use of LED- powered internally-illuminated signs might be considered (see section 11). If signs are to be externally lit, the signs should be raised to take into account the risk of vandalism.
5.4.4. Regulatory signs must be placed as near as practicable to the start of a restriction and it is preferable to place them on the back line of the footway, or the verge where no footway is present. They should not be placed right on the corner of the junction, or right on the kerb side. Signs at a junction should be set back from the road, where practical, to aid driver’s visibility when turning in to that road. Setting a sign in this manner makes it aesthetically more attractive, less liable to damage, and more readily visible to road users who need to see it. It may also be sensible to angle signs at junctions slightly towards the side road carriageway so that they can be seen by turning traffic (particularly at night where signs are not directly lit and need to be illuminated by headlamps).
5.4.5. The fixing bands that attach the sign to the support should be tight enough and of an appropriate design to stop signs slipping or twisting around, or being deliberately rotated to give incorrect information to drivers. Designers should ensure adequate consideration is given to f ixings/support for sign plates as this is one of the main causes of failure. Manufacturers should supply suitable and appropriate fixings in accordance with their own declaration of performance to prevent panel separation, twist or slippage, including appropriate torque settings.
So you can see the councils all so terrified of litigation if a pedestrian bangs his head on a sign mounted above a pavement, that they mount them beyond the tallest possible person !
