There are many ways to reduce the alar base. The wider the base it becomes more careful. Like the first picture; if the nostril is big because the alar base is big a part of the alar base (green squares)needs to be removed. However if the base itself is wide the alar should not be removed. In that case the interior side of the alar base should be pulled.
If both the alar and the base are wide both surgical methods should be carried out. The nostril can get reduced as much as one want as long as it's not as much to cause problems when breathing.
About the picture  below: red arrow is the alar base and the green square shows the incision area. If the incision is made following the groove then a serious scar will remain.

(DM)

아래사진에서 붉은색 화살표는 콧망울의 베이스 파란색 네모는 절제부위를 나타냅니다. 절제시에 콧망울의 홈을 따라서 절제를 하면 흉이 크게 남습니다.