About the blessing when donning the tefillin Orach Chayim 25:7 says:
יברך להניח בקמץ תחת הה"א ולא בפתח ובדגש:
He should bless lehaniach with kamatz under the hei and not with patach and dagesh.
וְרֵאשִׁית֩ כָּל־בִּכּ֨וּרֵי כֹ֜ל וְכָל־תְּר֣וּמַת כֹּ֗ל מִכֹּל֙ תְּרוּמ֣וֹתֵיכֶ֔ם לַכֹּֽהֲנִ֖ים יִֽהְיֶ֑ה וְרֵאשִׁ֤ית עֲרִסֽוֹתֵיכֶם֙ תִּתְּנ֣וּ לַכֹּהֵ֔ן לְהָנִ֥יחַ בְּרָכָ֖ה אֶל־בֵּיתֶֽךָ׃
And the first of all the first-fruits of every thing, and every heave-offering of every thing, of all your offerings, shall be for the priests; ye shall also give unto the priest the first of your dough, to cause a blessing to rest on thy house.
This is perfectly fine with respect to not geminating the n. Being an Ashkenazi, the Maharil obviously didn't have any problems with differentiating between kamatz and patach either. But what should Sefardim do, who don't distinguish the two vowels?
Coming from Bagdad, the Kaf haChayim understood the problem, and he proposed to lengthen the syllable, but in that case you may overcompensate and fail to put the primary stress on lehaniach. Did later authorities confirm his ruling? Or should Sefardi Jews make an effort to pronounce the two vowels in a different way?
Possibly related: Sefardi rishonim who differentiate between Patach and Kamatz