Problems with Lighmass solution....

Hello everyone…

I got really annoying problem with lightmass solution… Below I attached image with the highlighted moments… These edges should be darker…
I brought model from 3ds max using Datasmith… this planes are just seperate models… I solved this problem by just integrating mesh with wall (highlighted with green noundary)… but is it only solution?

I really appreciate for any answers
Thanks,

thank for reply… desk is made of closed geometry you can see it has thickness… Floor is a part of “shell” which surrounds the whole flat…

I am putting next screen which shows this strange behaviour… This problem is particularly annoying because this over-bright surface affects other surfaces…

thanks guys for response…
To bring more informations about the scene I am posting more screenshots of my scene. I am having really hard time with those overbrighten edges…