Shadow not extending to intersecting corner

[Jeric_Synergy]

In this image, the blue box intersects the green plain. However, the shadow does not extend up the edge of the box.

This is reminiscent of shadow-mapped shadows with insufficient resolution: is that the case here? If so, where is the setting to increase the resolution? Tnx.

[Hunkadoodle]

You might want to look into the Contact Shadows settings. See the manual page here: https://docs.blender.org/manual/en/latest/render/eevee/lighting.html#contact-shadows