mirrored reflection and caustics

[francois.giard]

Hi

I am trying a simple setup and cant seem to get it working properly : sunlight gets inside a box and hit a mirror surface. So I have a box (standardSurface) and a mirrored plane (standardSurface w thin film mirror glass, and activated caustic). If you look at the result image you can see some caustic hitting the ceiling but it doesn't look at all as what I would get in real life. Faking it with Gobo wont help, looking for have true calculation of where caustics hits the surface.

Any Solution?

Thanks in advance. -François