Hi dade, here are additional tests and comparisons with pure caustics lighting.
Luxcore white shadows
interestingly luxcore is trying to build caustics behind glass
Maxwell white shadows (hidden from global illumination)
interestingly maxwell il able to add a decent amount of light behind the glass.
But this light has not much to do with the original beam you notice if we hide the glass, see last picture.
Luxcore normal shadows
interestingly this rendering is almost identical to the white shadows one, just a bit noisier.
Maxwell normal shadows
It seems that the physically correct Maxwell do not even tries to let the caustics through
Luxcore and Maxwell no glass, same result.
The amount of light lost because bad caustichs calculations can be relevant.