Quote - ...on that point, how high should the camera be, ideally, do folk reckon??

Since we must choose, I think just a smidgeon above crotch height is the thing to go for. This will allow a whole standing figure (+hair) to be framed with an approximately equal amount of space above the head and below the feet when the camera is held level with the horizon.

So to put some approximate numbers on this:

0.36 PNU
944.0 mm
37.0 inch

The above is based on the height of the Antonia Polygon figure (roughly 0.7 PNU). In the attached image, the camera is horizontal. If it were any higher or lower, it would start to cut of the feet or head unless it were tilted.

Whilst the above value may be the best general compromise, it certainly would not hurt to have some variety. I sometimes have the camera at knee height or lower, this can be good for glamor, fashion, or action scenes. Or sometimes I like to have the camera at eye height, which can be good if you want to to portray interpersonal stuff between two characters. An even higher POV can be good if you want to portray a group of people, or relationship to the environment.

And I definitely agree with aRtBee, that "for each HDR result it should be clearly documented how high the camera was above the ground when the render was made", perhaps the value in cm or inches could be included in the image file name?