Gemara

49b - Beraisa: He piles (the Ketores on the coals) in order that the smoke will not come too quickly;

Some say that he scatters it (on the coals) in order that the smoke will come quickly.

52b - Mishnah: He piles the Ketores on the coals.

Our Mishnah is like the opinion that he piles it.

Beraisa #1: He piles the Ketores on the coals (on the) inside (the side closer to the Aron) which is outside (further away from) himself;

Contradiction (Beraisa #2): He piles the Ketores on the coals outside, which is the side closer to himself.

Answer (Abaye): Tana'im argue about this.

Abaye: Presumably, the Halachah follows Beraisa #1:

(Mishnah): We instruct him (the one selected to be Maktir the daily Ketores) not to start dropping Ketores in front of himself, lest he get burned.

Tamid (6:3): We instruct him not to start dropping Ketores in front of himself, lest he get burned. He began to flatten out, v'Yotzei.

Rishonim

Rambam (Hilchos Avodas Yom Kipur 4:1): With his hands he piles the Ketores (of Yom Kipur) on the coals in the inner side of the Machtah closer to the Aron and further from himself, so he will not get burned.

Ri Korkus: Rashi says that he begins to pile it at the end of the Machtah and pulls his hands back to himself, constantly (dropping and) piling Ketores on the coals, until reaching the end of the pan. The Rambam does not mention this. He holds that all was piled at the end of the Machtah.

Rambam (Hilchos Temidim u'Musafim 3:8): We instruct the Kohen not to start dropping (the daily) Ketores in front of himself, lest he get burned. He begins and casts the Ketores on the fire gently like one who sifts flour, until it is spread over the entire fire.

Question (Aruch ha'Shulchan ha'Asid 105:18): Why does the Rambam say that he spreads it like flour? The Gemara says that he piles it in order that the smoke will delay to come!

Note: The Gemara brings another opinion. Perhaps the Aruch ha'Shulchan assumes that the Rambam rules like this opinion, for he says that the Ketores is dropped in a way that he will not get burned.

Bartenura (Tamid 6:3 DH she'Lo): He would pour the Ketores on the coals in the west; when they scattered towards himself he would pile it up. The Gemara (Yoma 49b) says that this is done so the smoke will not come too quickly. He piles the Ketores on the inside, which is further from himself; like the Gemara in Yoma (52b).

Question (Tosfos Yom Tov DH she'Lo): The Bartenura means that even though he tried to pile the Ketores in the west, if some scattered towards himself he would return it to the pile. However, the Mishnah says that he was Meraded, which means to flatten out!

Answer #1 (Tosfos Yom Tov): Rather, we must say like Rashi (Yoma 52b DH Tani) who says that he (drops and thereby) piles Ketores starting in the west, and continues to do so while drawing his hands back to himself.

Answer #2 (Rashash DH v'Da): Rather, all agree that he spreads out the daily Ketores. Only regarding the extra Ketores of Yom Kipur there is an opinion that he piles it. The Rambam mentions piling Ketores only regarding Yom Kipur, not regarding the daily Ketores.

Sefas Emes (52b DH Tanan k'Man): The Rambam holds that all agree that the extra Ketores of Yom Kipur is piled. The argument is about on which side he piles it. The Rambam holds like Tosfos (53a DH she'Lo) that Abaye supports himself from a Beraisa that discusses Yom Kipur, and not from the Mishnah, which discusses the daily Ketores.

Question: The Mishnah says he began piling, and immediately says 'v'Yotzei' (he leaves). When does he finish? Also, the Seifa says that he burns it and leaves (it never mentions that he returned)!

Answer #1 (Rosh): 'V'Yotzei' means that he removes his hands.

Answer #2 (Rashash DH Hischil): 'V'Yotzei' refers to the one instructing him.