51. The genitive plural shows an exception to the rule of noun accent. The rule of noun accent would require the accent to remain on the same syllable as in the nominative singular. But nouns of the first declension have a circumflex on the ultima in the genitive plural no matter where the accent was in the nominative singular.
...
62. Learn the declension of μικρός, small, and of δίκαιος, righteous (in §569, §570). Note that long α not η stands in the feminine of these adjectives when the preceding letter is ρ or a vowel (compare §55). The accent in the genitive plural feminine of all adjectives of the second and first declension follows the regular noun rule and not the special rule for nouns of the first declension (§51).