You got more room during the dark part of your ride precisely because the motorist did not know you were a cyclist and were afraid that the flashing light was something that could really damage their car.

It use to be that way for me as well on an unlit stretch of highway. As the same motorist became use to seeing my lights, they quickly learned I was a cyclist that could only do minimal damage to their cars. As such, they began passing closer and closer over time. Motorist are extremely poor judges of lateral separation at night.

As it stands, motorist give me way more room in the day than they now give me at night, opposite of what use to be true. So the theory of “safety in numbers” is not working for me.