Thanks, Rotund!
I do that a lot, in fact, but for some stuff I find I like to have more control over the attack/release of the ducking than a side chained compressor will afford me.
On the other hand, I usually duck to about the same gain levels, and of course always will return the M+E to 0 dB after the narration passage. And I’m sick of fine-tuning automation at that point, when I wouldn’t have to.