Descriptor sampling pattern size

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OpenCV keypoints have a bunch of attributes of which two are octave and size.

1. Is the descriptor sampling pattern size (from e.g. BRISK or FREAK) defined by those two attributes? If yes, does this mean that if I detect the same physical point in the same octave layer by two different detectors, the descriptor will not be identical?
2. Do descriptors always use this size information or is this optional?