First graphic shows our Moon to the actual described sizes of Eberron's moons. Later on there is a graphic of their apparent size compared to our Moon. Zanatyr for example is roughtly half the size of Earth's moon, but would appear to be 9 times larger in comparison.
I think there's an issue in the calculations.
The radius of an orbit is typically given from center of the parent body to the center of the satellite.
The apparent size of the satellite is determined by the distance from the viewer, to the center of the satellite.
The "D" in the equations above, then, is the radius of the orbit minus the radius of the PARENT body.
So, we note that in the discussion of Zarantyr, we'd need to know the radius of Eberron, not the radius of Zarantyr.
Mind you, usually, in the real world, the orbital distance is very large compared to the radius of the Parent body. For example, the radius of the Moon's orbit is something like 60 times the radius of the Earth - if you just neglected the Radius of the Earth, your D would be off by less than 2%.
If you are looking for a ballpark - just use the Orbital radius, and never mind the rest.