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The geometry will reduce the accuracy of the fix though as all the satellites will be in the same 8 degrees of the sky.

I wish they had said in the article what the accuracy is!

Is 8 degrees the angular size of the Earth from the moon? Aren't GPS satellites in relatively high orbit, so it could potentially be a larger patch of sky.

I hadn’t realized it, but you are right.

- Orbit height: 20,200 km

- Earths diameter: 12,760 km

https://www.gps.gov/systems/gps/space/

https://science.nasa.gov/earth/facts/

It’s the satellites’ size.

The satellites are 20 Mm high above the ground so their spread is 53 Mm, which is 4.4 times the diameter of the Earth (12 Mm). So yes, the angular size of the satellite cloud (7.896°) is quite a bit larger than the Earth (1.785°) from the moon PoV.

Although since the GNSS satellites use directional antennae pointing at Earth, this experiment only picked up signals where the satellites are on the other side of Earth and close enough to its edge for some of that directional signal to leak past the edge of Earth and get to the Moon. So, the satellites that are nearly 4° away from the centre of Earth cannot be detected because they are beaming their signal nowhere near the Moon, and the detectable angular size is much less than 7.896°.

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