Where exactly, were the rings fixed?
Panim Yafos: The rings were on opposite corners. However, the Kohen put blood on the corner, from the top and ran his finger down the edge (Yuma 58b)! We must say that the rings were above the Mizbe'ach. 6
See Oznayim la'Torah (citing the Ha'amek Davar).
Even though in other places "Tzal'osav" means 'sides', here it means 'corners' - since the Torah already wrote "Al Sh'nei Tzidav".
Not a third of the way down, like the other Keilim, since due to its light weighjt, this was not necessary.
Bearing in mind that the Mizbe'ach ha'Ketores was square, it is not clear what it means by 'the width'?
The Seforno translates "Tzidav" as the sides that comprise the width and Tzal'osav" as the vertical walls.
Perhaps Yoma 58b discusses in the Beis ha'Mikdash, which did not have rings! Perhaps it is logical that putting the blood was the same in the Mishkan and in the Mikdash. (PF)
The Mizbe'ach was only one Amah wide, so there was only one Amah between the poles. How could two people fit inside to carry it? We needed to say that the length of the Aron was between its poles, for two people could not fit inside the one and a half Amos of its width! (Refer to 25:12:1:1.)
Da'as Zekenim, Hadar Zekenim, Riva: Only one Levi carried it in front, and one in back. He stood in between the poles. 1
Panim Yafos: The rings were on opposite corners, so there were 1.4 Amos between the poles. This was enough for two people.
Panim Yafos (Bamidbar 7:9): It says that they carried ba'Kasef (the known shoulder. i.e. the right one). We must say that one Levi stood outside the poles (on the left), and one stood between the poles.
Perhaps two people carried it, and each stood outside the poles. According to the opinion that Leviyim were 10 Amos tall (Shabbos 92a), there is barely room for one person's head to fit between the poles! (PF)
Panim Yafos: The staves would be outside his shoulders! (Coffins fit into hollows in burial caves an Amah wide (Bava Basra 101a). This includes the width of the walls, and they must hold also wide people! Sukah 8a brings opinions that people are (a) one Amah, or (b) two thirds of an Amah wide; perhaps the former opinion included space between adjacent people. - PF)