From the explanation of the Gra"z (in his Pesach commentaries there), behold, the Rambam added in this halacha that if one indulges in other foods during the meal, it is praiseworthy. It implies from this that the main principle of leaning refers to the entire meal of the night, and is not specifically for the mitzvah of matzah, but in the eating of the matzah, there is an obligation to lean. This is the law concerning the eating of matzah, but not in the actual fulfillment of the mitzvah of matzah. The source for the Rambam's opinion is brought from the words of the Jerusalem Talmud (Pesachim chapter 10, halacha 1): "Rabbi Simon said in the name of Rabbi Yehoshua ben Levi, that olive-sized portion with which one fulfills the obligation on Passover, one must eat it leaning." And if we were to say that the obligation to lean applies to the actual fulfillment of the mitzvah of matzah, the Jerusalem Talmud would not have needed to use the phrase 'that olive-sized portion,' because that is obvious, for after eating the olive-sized portion, there is no longer an obligation of matzah. What does it imply to us? It must be that he is referring to the mitzvah of leaning on its own, to fulfill it in the first olive-sized portion of matzah, and in other eatings, if one fulfills it with leaning, it is praiseworthy.