feudal estate
寀 centers on a feudal estate: a landholding granted by a lord, including the territory and the official position tied to it.
寀 combines 宀 (roof, building) with 采, which likely contributes the sound and relates to picking or selecting, perhaps referring to an allotted estate or office.
Under a roof 宀, the 采 component suggests picking or selecting land. Imagine a lord selecting a piece of land and putting a roof on it to mark his feudal estate.
For サイ, picture a feudal lord sighing with satisfaction as he surveys his estate: sigh -> サイ, and the roof 宀 shelters his chosen land 采.