Yes, shows my age a bit. The term "precision" is today (well inside the era of 2D/3D nomenclature) defined by the delivered performance (result) as opposed to my education time when it was directly describing the technology. Precision = vertical guidance provided by electronic means, and the light beam does exactly that. I may have used the equal sign there illegally.
To my knowledge, EW propagation don't change over time, surely still the first 1-6m of GP pattern is bent and the GP plane ground intercept is not exactly co-located with GP antenna spot. In that respect the graphic (from "flight crew" manual) is good enough to suggest a box where the ideally-straight GP comes from, upwards. The ground around the antenna needs special focus, some pictures show it.
The Airplane Flight Manual's 50-feet&3-deg ground intercept is defined as 50/[tan(3deg)] = 291,78 m (past the threshold) for the geometrical plane - and the engineers do their magic to align the GP signal to ... ehm ... close to there most of the time.
Well visible on the following :
+ distance marker 300 m
+ 3 deg plane somewhat shorter than 300 m
+ GP antenna anchored a little further to allow for GP bending,
