The Mishna Berura says in three places (that I know of) that every birchas hamizvah must be said standing up (סי' ח' ס"ק ב', סי' תפט שעה"צ ס"ק ז', וסי' תקפה ס"ק א-ב). If this is true, why doesn't anyone stand for the bracha of leshev basuccah other than by kiddush, like when they are having a snack over chol hamo'ed?
Perhaps the reason is that without sitting there's no kviyus and you shouldn't be making any bracha, which would not be the case on Shabbos/Yom Tov when it's muchrach that you'll stay for the seuda (see Aruch Hashulchan O"C 166:1)?
Any insights and/or mareh mekomos would be greatly appeciated.