Yeah I agree, see this post specifically: The proper way of calculating lux / cd / candlepower - #35 by EasyB
I made that thread to explain the concept that I read about on CPF, but after some further research it seems to be incorrect.
The light coming out of a lens is not a single cone of light that diverges from one point, it is an infinite amount of light cones coming from the surface of the lens.
See image 5: Light collimation with an LED flashlight
Based on this, the total lux of the flashlight is simply the sum of all these cones of light.
Since each cone behaves according to 1/d^2, then the sum of all cones also behaves proportional to 1/d^2
So in fact the light converges at the lens, not behind it.