What's the reason for the local flap extensions at the shockbody locations?
The anti-shock bodies also serve as fairings for the flap actuators. When the flaps are extended, the anti-shock bodies move down as the flap mechanisms extend. The upper surfaces of the anti-shock bodies are open to allow room for these mechanisms to extend.

The extensions to the flaps are to cover the openings of the anti-shock bodies when the flaps are retracted to provide a more aerodynamic surface. Evidently the outer locations have larger openings to cover.

Below is an image of a different aircraft and flap track design, but the principle is the same. You can see some of the hardware that sits in the fairings, and the covers that allow the hardware to extend out of the fairings.


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When the flaps are retracted, you can see that the flaps close out the top of the anti-shock bodies, and the outer position is closed out further aft.


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