OK here's a bunch of rough calculations that show the Moon wasn't in the plasma sheet while the Apollo Nov astronauts were there. Doesn't say anything about the magnetotail in general which is all vague and big.
Data:
Thickness of plasma sheet: 6 Earth diameters
Distance to moon: 30 earth diameters
Date of landing: Nov 19 1969
Date of leaving: Nov 21 1969
Date of full moon: Nov 23 1969
Period between full moons: 30 days
The angle between the moon and the line straight away from the Sun is 0 degrees on Nov 23
It's about 20 degrees on Nov 21 (23-21)/30 * 360deg
It's about 50 degrees on Nov 19 (23-19)/30 * 360deg
The angle between the edge of the plasma sheet at the moon's orbit, and the line straight away from the Sun is arctan(3/30) = 6 degrees.
So, the sequence of events would be:
Land on moon at 50 degrees
Leave moon at 20 degrees
Plasma sheet hits at 6 degrees
Full moon at 0 degrees
Therefore the astronauts weren't on the surface inside the plasma sheet.
