【light source angle】 can't affect area shadowing from DFshadows.WHY?

In the two screenshort below,the “light source angle” are set to 1 and 5,but the area shadowing don’t change:
The directional light is set to stationary,and CSM is disabled,the light is rebuilded everytime.

https://forums.unrealengine.com/filedata/fetch?id=1639700&d=1562577863

https://forums.unrealengine.com/filedata/fetch?id=1639701&d=1562577915

Settings:

https://forums.unrealengine.com/filedata/fetch?id=1639702&d=1562577917

https://forums.unrealengine.com/filedata/fetch?id=1639703&d=1562577951

https://forums.unrealengine.com/filedata/fetch?id=1639704&d=1562577958

Mesh Distance field:

https://forums.unrealengine.com/filedata/fetch?id=1639707&d=1562580327



But when I set directional light to static,the area shadowing is OK.:

https://forums.unrealengine.com/filedata/fetch?id=1639705&d=1562580080

https://forums.unrealengine.com/filedata/fetch?id=1639706&d=1562577919

Why???
Is this a BUG?