Momentum bar = x2 previous bar.
Those happen on reversal and act often as a engulfing candle, and as you said, "delta zone" could be consider 0-50% from opening of the bar = reversal area, witch is wicked most of the time before next move in the same direction as momentum bar.
http://cdn.forexfactory.com/attachme...1&d=1250880754
Later!