TT #68 · Parshas Shemini · Aliyah 3 · Passuk 12
Chabad.org — Vayikra Chapter 10 with Rashi
English: “Beside the altar”: the phrase means beside the altar, not in the Sanctuary and not on top of the altar.
Sifra (Toras Kohanim), Shemini, Chapter 1.
Sefaria — Sifra, Shemini, Chapter 1
Geographical limitation — the phrase “beside the altar” excludes eating in the Sanctuary proper and on top of the altar.
The location for eating the remaining meal offering is restricted to the area beside the altar, not in the Sanctuary proper and not on top of the altar.