long kimono
袁 centers on a long, flowing robe or kimono, specifically a traditional garment that trails or drapes. The meaning is narrow and concrete, without strong abstract extensions.
袁 is traditionally explained as a pictograph of a long robe, with the top suggesting a head or cover and the lower part representing the flowing garment. The exact historical development is uncertain, but the association with clothing is well established.
The top 土 over 口 looks like a head and collar, and the lower part resembles the long, trailing hem of a kimono. Picture someone wearing a floor-length robe that sweeps behind them.
For エン, imagine the long kimono ending in a graceful curve: end -> エン, and the robe's hem trails to the end of the room.