sphere, circle, radius, range
圈 centers on a bounded circular area: a sphere, circle, or radius, and by extension the range or scope within a boundary.
圈 combines 囗 (enclosure) with 卷, which likely contributes both sound and the idea of rolling or curling, suggesting a bounded circular space.
The outer 囗 is a boundary, and inside is 卷, which looks like something rolled up. Picture a rolled-up scroll inside a circular frame, defining a sphere or range.
For ケン, imagine a ken (a Japanese unit of length) used to measure the radius of a circle: ken -> ケン, and the circle is enclosed by 囗.