From my reading of the changes in the iOS 8.x SDK, the application cannot detect that the user has activated Reachability. I think that Apple wants (and expects) that this feature will simply allow access to the upper half of the screen and completely transparently transfers the movement of the base view to the application. I can not point you to any specific documentation on this subject, as this is a case of lack of evidence, which is the evidence itself.
Oh, and I don’t think that Apple wants any application to do something “unexpected” when Reachability is activated !; -)
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