Dark side of mesh has full shadow strength instead of value from directional light

Apologies in advance, but I'm completely new to lighting and shaders and such.



I have a directional light coming in from the right. There is an invisible ceiling blocking it, so that the entire interior is covered in a shadow. The B shadow on the wall and B shadow on the grass are the same, set by the light's shadow strength property (let's say 0.5). The problem is A, which is equivalent to if I set the light's shadow strength property to 1.0.

Where would I start if I wanted A to respect the light's shadow strength property so that it matched B?

 

You probably don't want to touch the shadow strength and it should really be kept at 1.0 no matter what. What you need to emulate lighter shadows is probably just more ambient light.