Rashi on Numbers
בתוך מטותם [AND THE STAFF OF AARON WAS] IN THE MIDST OF THEIR STAVES — He placed Aarons staff in the middle (בתוך) in order that people should not say, “It is only because he placed it at the side where the Shechinah is that it blossomed” (Midrash Tanchuma, Achrei Mot 8 on אחרי מות).
Rabbeinu Bahya
ומטה אהרן בתוך מטותם, “and Aaron’s staff among their staffs.” [בתוך מטותם can be translated "in the middle of their staffs." The other tribes’ staffs were placed surrounding that of Aaron] so that it could not be argued that this miracle occurred because only his staff had been deposited near the Shechinah.
Siftei Chakhamim
In the middle. Once the Torah writes “twelve staffs,” why is it necessary to say that “the staff of Aharon was among their staffs”? Rather this was to teach that before he placed them in the Mishkon, they arranged the staffs before them and Aharon’s staff was placed in the middle. Re’m writes that Rashi may have found Midrashic support for his words, and it is not that the word “among” indicates this.