Now that I'm actually looking at the calculation, I noticed something.
The expansive truthseeking orb is actually...
hollow? AKA volume doesn't really apply since the vast majority of it is... air?
You can see when it is collapsing that it's unraveling in the manner that it's collapsing upon itself, to where the inside of it doesn't showcase nearly enough volume for a "non hollow" sphere of that size.
This isn't something that is manga conjecture only. The anime showcases it heavily as well,
showing a shot from inside of the truthseeking orb watching the outside break apart, then showing only the outsides of the orb break. Alongside that,
it showcases the outsides of the orb comprising the entire orb. There is nothing on the inside because it it hollow.
The lighting is explicitly taking that pathway because it shines on the forward surface portion and not in the inside. There would be no need for shadows for the inside if the inside was full. There would be no inside to begin with. The orb is... well, not full.