Cool ! You are reaching a typical artistic problem with flat surface lighting in those kind of games: Surfaces front to the lights are brighter than others. I think it's very visible on the first image. The walls are brighter than the floor and it become even worse with fog.
I suspect it's related to color linearization: before do lighting computation linearize your values with pow(value, 1/2.2), then do your lighting computation, then do a pow(fb_value, 2.2) on the whole frame buffer. The lighting contrast shoud be less visible. It's then up to you to use a nice curve for frame buffer output.
You can also keep the current way as an assumed retro style. :)
Keep the good work.