you can also turn up the diffuse boost on the floor material and this will increase the amount of reflected rays from the lights hitting that material.
thanks a lot for all you reply. I solve a part of the problem by reducing a lot the Lightmass Importance volume. Now it fit the house (and not the whole landscape). I rebuilt with production light, here some screenshot: Light Only: Unlit: Texel: full render: Interior, light only: The problem is to have a nice exterior…