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What is happening here is that the less the proximity of any two tones played in succession, the greater the ambiguity in terms of height. This principle can be better comprehended with the following visual aid:

Each of the 12 tones in the octave are shown.  C is shown at 12:00, C# at 1:00, and so on. Tonal ascension is achieved with clockwise movement; tonal descension is achieved with couter-clockwise movement.