Feature of Size Flatness

In this Question Line video, Jason answers the following question regarding Features of Size and Flatness: 

In my understanding, when a straightness or flatness tolerance is associated with a FOS, the Rule #1 is overridden and perfect form at MMC is removed. So, straightness or flatness tolerance associated with a FOS can be greater than the size tolerance.

However, in Y14.5-2009, the standard says that with flatness of a surface, where the considered surface is associated with a size dimension, the flatness tolerance must be less than the size tolerance. Why must the flatness tolerance be less than the size tolerance?

In this video, Jason compares two drawings, shown above. The first drawing has flatness directly applied to a planar surface which is utilized with a size dimension. The second drawing has flatness applied to a size dimension. Jason explains for each example what elements are being controlled by flatness. He also discusses why Rule #1 is overridden in the flatness of a feature of size example, and also how flatness applied to a surface associated with a feature of size affects that feature of size. 

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