If you at/near approach idle thrust, arent you supposed to spool up at the MA location?
This timeframe in the discussion, if ref engine spoolup alone, is a bit troublesome from a procedure design perspective.
The momentary descent (50 feet) was based on a 7 second reaction time.
The reaction time included pilot decision making to GA of 2 seconds, 3 seconds for the action to place the ac in GA mode, and 2 seconds for the aircraft to react...
This discussion seems to say that it takes 6-8 seconds for the engine to go from approach idle to GA thrust.
That means 11 to 13 seconds for the ac to react...that is a hell of a lot more than 50' of momentary descent.