These 'reversed' tone letters are used to indicate tone sandhi. For example, ˧꜖ after a word or syllable indicates that it has a mid tone in isolation, but a low tone in the current environment.
When this letter occurs in ligature with other tone letters, they together indicate the pitch contour of the tone. For example, ꜖ means a level low tone, and ꜕꜖꜓ means one that begins mid-low, goes low and ends mid-high.
Tone letter on Wikipedia.Wikipedia 