When Thai contour tones sit on long and short vowels followed by a nasal consonant, different portions of the tone are superimposed on the vowel and the nasal: more of the contour on a long vowel and less on the shorter following sonorant and vice-versa with a short vowel. This change, which we call ‘phase realignment’, presents some complexities because overall the tone is shorter on the rhyme with the short vowel and in other situations the strategy of fitting tones to segmental sequences of varying duration involve truncating one end of the contour. We report here our attempt to quantify this variation and to validate that the modification is just a realignment of different parts of the tonal contour with the segmental sequences it sits on.