Rich wrote:

And L1 is about 4x the current lunar distance. Given that an eclipse
at the current distance sweeps a narrow path across the earth it
would seem that the moon at that distance would provide very little
shade, if any.

L1 is unstable, so keep shades there would require active stabilization,
probably involving light pressure.

You don't need a full shadow to reduce insolation at the Earth;
a shade that appears smaller than the sun's disk, as seen from
Earth, would still reduce insolation at Earth. What you'd want
is the shade placed so that for every illuminated spot on Earth,
the shade was fully in front of the sun as seen from that spot.

Paul