I did actually manage to use the spray on my lower back today, after a bit of twisting in front of the mirror.
As to the dose, the manufacturers are meant to be updating the leaflet, but by the sounds of it, even they don't know what it is!
The leaflet suggests that you get the same dose per spray, but I don't see how that can be because some sprays provide enough liquid that it runs, and some don't.
Fortunately I don't seem too sensitive to the variation, but I imagine it is hard if you are sensitive to it.