I mean, compared to the distance to the moon, yeah - 40km is a rounding error. I don't care if I'm measuring the distance to the moon from my location or 40km

I mean, compared to the distance to the moon, yeah - 40km is a rounding error. I don't care if I'm measuring the distance to the moon from my location or 40km away. And that's 4x less of a difference than your 20 light-year example (moon is ~10,000x further than 40km). Choosing "from us" seems more than precise enough.