Revit has an interesting quirk in its geometry engine that causes it to report the luminaire as being contained within the space, if the photometric web graphic intersects the space (even if none of the physical geometry is in the space). See below.
Fortunately, this often won't be a major problem. If the extra luminaire is on the other side of a wall, the wall will block the light reaching the calculation points. So the affect to the final numbers can often be negligible. A bit of extra light will "leak through", due both to numerical precision issues and the implementation details of the calculation engine. If you need to be 100% certain the extra luminaire isn't skewing the numbers, one work-around is to "switch off" the offending luminaires before calculating.