As ghostdigital said, flatness specified to a surface is a refinement of the surface and it must be less than the size tolerance.
The only exception I can think of is that with a long plate, I can apply a flatness to the thickness dimension to override rule #1 and give it a bigger flatness...
In my understanding, when a flatness tolerance is associated with a FOS, the Rule #1 is overridden and perfect form at MMC is removed. So, flatness tolerance associated with a FOS can be greater than the size tolerance.
However, ASME Y14.5-2009 specified in section 5.4.2 that, with flatness of...