lopsided

咼 is composed of 冎 and 口(mouth). 咼 is the picture of a skull, a skull is a bowl shaped bone, while 口 emphasises the concavity of the skull, for 剮, 窩 and 過, we learn that the exact meaning of 咼 should be concavity, which has the same meaning as 窩, but in Shuowen Jiezi(說文解), 咼 means lopsided, why?