[Slim Pickens]

Well, from the numbers you've presented, it sounds like an adjustment is necessary. There are two factors unique to SNG poker that would seem to make this M=5 rule-of-thumb for the red zone too high for a SNG tournament.

1) The blind structure is, relative to any live tournament Harrington might ever play, insanely fast on a per hand basis.
2) You always have the option of beginning a new tournament immediately after busting, so there's no premium on the "opportunity" of remaining in the current tournament.

I've actually got a use for a quantity like the one Harrington gives if it could describe, in one number, a player's exact situation in a tournament independent of stack size, blind size, and the number of players at the table.

Anyway, my opinions...
Q1) This needs to be adjusted for SNG's.

Q2) It might be valuable to include the namber of hands before a player posts blinds and the number of hands remaining in a level (in some unknown ratio) in M. I like this idea and I want to think about it some more.