Dynamic shadow view distance limit comes from two and only two parameters. The first is dynamic shadow distance. According to your screenshot, the objects, beyond 20000 range the only source of dynamic shadow you will have is far cascade, that is stretched from 20000 to 300000. That low resolution cascade is simply incapable of displaying a shadow for a such small objects. It will be filtered out.
Secondly, there is a feature, where objects, smaller than certain threshold on screen, will not cast shadow. It is controlled by r.Shadow.RadiusThreshold. In your case, it means that anything, that occupies less than 1 percent of the screen, will not cast shadow. Feel free to reduce it by a few orders of magnitude.
That is it.