That is a good explanation, Michael.
I am not doing macro but yesterday I made a graph based on my earler post.
The vertical scale is 'relative EV" to indicate change in camera settings for example f/ (by taking log-base2 of the change in luminance [cd/m^2]
Graph is for a 65mm long flash tube.
It also shows that after the distance is further than 2~ 3 times the length of the flash tube, the Gauss Law (inverse square)
is quite accurate.
Closer than that, the EV settings do not change so much.