Did the Kohen Gadol wear the same garments his predecessor wore, going back to Aharon HaKohen, or did he have new garments specially tailored to fit him? In other words, were the garments each Kohen Gadol wore the exact same garments Aharon HaKohen wore?
If they were the same garments Aharon HaKohen wore, then perhaps there was some sort of miracle that happened that allowed the garments to fit each Kohen Gadol, despite their varied sizes and shapes. (We know for instance that Eli HaKohen was very fat.)