Zone system in digital context?

[I'm afraid this question is oriented more to the stratum of people in
this newsgroup who prefer a "more precise" mode of communication...]

When you THINK about zones in digital context, where do you put the
saturation point of the sensor? I see two logical choices: the middle
of zone IX, and the right edge of the zone IX. Since they differ by
40%, in some contexts it could make a difference.

Myself, I use the middle. What do you use?

[Of course, when making an actual shot, this question is moot; just
adjust to the actual subject, so nothing which "has a remote chance
of being important" is overblown. I'm thinking more about a context
of a "discussion on r.p.d", not actual shooting.]

Thanks,
Ilya