I’m guessing this is related your other forum post: Different sky for reflections . Normally roughness values between 0.01 and 1 result in different level of roughness, but for uniform surroundings, such as a white sky texture, this different level of roughness will look the same. The surrounding captured in light probes is blurred with different levels of blurriness, the rougher surfaces use the most blurred levels, the smother surfaces less blurred levels. If the surrounding is uniform, all these blur levels will look the same (white in your case).
As for the reflection strength, we consider taking sky strength into account when calculating reflections. For now the sky strength is used only for baking (it is constant for reflections). The sky strength should allow to limit the reflection and is a physically based parameter. I’m not sure if reflection strength has physical interpretation. UPDATE: I forgot that you can already control reflection sky strength if you use HDR sky image in HDR formats (.exr, .hdr), in such case strength from the format is used.