By default, the world אַתָּה (you) has a final stress. If I am correct (and the concordance as well), out of 172 occurrences 159 satisfies this rule in the Torah (92%).* However, if this word is in a pausal position, the stress is withdrawn to the penultimate syllable (Bereishit 29:14):
וַיֹּ֤אמֶר לוֹ֙ לָבָ֔ן אַ֛ךְ עַצְמִ֥י וּבְשָׂרִ֖י אָ֑תָּה וַיֵּ֥שֶׁב עִמּ֖וֹ חֹ֥דֶשׁ יָמִֽים׃
And Laban said to him: "Surely thou art my bone and my flesh." And he abode with him the space of a month.
I have counted 7 such cases (4%). Yet, right in the next verse we see:
וַיֹּ֤אמֶר לָבָן֙ לְיַֽעֲקֹ֔ב הֲכִֽי־אָחִ֣י אַ֔תָּה וַֽעֲבַדְתַּ֖נִי חִנָּ֑ם הַגִּ֥ידָה לִּ֖י מַה־מַּשְׂכֻּרְתֶּֽךָ׃
And Laban said unto Jacob: 'Because thou art my brother, shouldest thou therefore serve me for nought? Tell me, what shall thy wages be?'
I have found 6 cases where there is a patach despite the penultimate stress (Bereishit 3:19, 22:12, 29:15, 32:17, 49:3, Shemot 33:3). 5 of them have zakeif katan, 1 has pashta. Aren't these disjunctives strong enough to warrant a kamatz? Does it happen due to a nasog achor? Are these cases simply exceptions?
* I have considered the words: אַתָּה, וְאַתָּה, אָתָּה, וָאָתָּה.