Excellent question, the Kitsur Shulchan Aruch here addresses a point which is not apparent in Shulchan Aruch in hilchot Chanuka.
See Mishna Bikkurim 1, 4. This Mishna says that a convert cannot read mikra Bikkurim because he cannot say "the country which the Lord swore to our fathers to give us" (Deuteronomy 26, 3). When a convert prays alone, he says "the G-d of the fathers of Israel" . When he prays in synagogue for the congregation, he says "the G-d of your fathers". Commentators on the Mishna report that in Talmud of Jerusalem the conclusion follows a Berayta that says that converts say "the G-d of our fathers" and read mikra Bikkurim because the land of Israel was given to Avraham who is the father of converts. Rambam rules as this Jerusalem's Talmud.
But for Vidui maasser it is different. Convert cannot say "and the land which you have given us, as you swore to our fathers, a land that flows with milk and honey.“ (Deuteronomy 26, 15).
Some Rishonim and poskim acharonim see no difference and concluded that convert bless. But if we want to understand the Rambam we need to understand why in mikra Bikkurim he rules that convert says the verse mentioning the land and the fathers and in Maasser sheni, he cannot.
Rabbi Meir Itschaki on Rambam Maasser sheni 11, 17 writes in name of Rashi on Chumash explains the difference. Rashi points that for the verse of Maasser Sheni the Mishna needs to quote the verse up to "milk and honey". The REM on Rashi explains that the mention of "flows milk..." was a swore said to the generation which get out of Egypt. Not to Avraham. In the same way regarding Al Hanisim. The commentators on Rambam report Shut Shaar Efraim 14 with two answers to the contradiction in Rambam (First teruts: for Vidui Maassrot the Vidui contains a prayer, and for a prayer one needs to feel wholly each word. As in some periods people didn't say Gadol Gibbor and Nora in prayer. But for mikra Bikkurim the recitation is a praise and no problem. BTW the blessing of Sheassa Nissim is also a prise as mikra Bikkurim and we can understand the Shut Harambam quoted by @mevaqesh in which Rambam says that the convert can say laavotenu. Second teruts by the son of the author: in Bikkurim the point is on the promise to give the land to the whole Israeli nation but in Maassrot) the point is on the personal ownership) and the Shut Shay Lamora 54 (the teruts he retained: maasser the accent is on the actual giving of the land. In Bikkurim the accent is on the promise. potentially all descendants of Avraham were able to receive a part of the land. But those who reached Israeli people after the division of the land or who were excluded as the tribe of Levi did not get any part. They are linked to the promise but not to the division. No problem for mikra Bikkurim. Indeed for Vidui Maasser, we search an actual part. E. g. for Leviim Rabbi Yose says that they make Vidui because their ownership of Are Miklat. Second teruts, the gift pointed in Bikkurim is the fruits of the land, not the land. But in Maasrot the land itself is pointed) . I hope to find time to explain their Teruts. A master piece of the Suggia is the Tosfot Baba Batra 81a with the opinion of Rabenu Tam regarding Zimun for a convert.
(The Peri Megadim Eshel Avraham OC 186, sk 1 addresses the question of convert regarding second blessing of Birkat Hamazon.)
Even if we follow the Rambam, regarding the miracles of Chanukka, they were not made at the time of Avraham. So, possibly, in Al Hanisim we expect that a convert says "the miracles you made for fathers of Israel", not "our fathers". But this pilpul is not inescapable.
Conclusion: The KSA understanding of Sheassa Nissim disagree with the two terutsim of the Shaar Efraim and the tertsim of the Shay Lamora in Rambam, but is congruent to the Teruts of Rabbi Meir Itschaki in Rambam.