In the chandas (Vedas), a single consonantal sārvadhātuka affix gets diversely the augment after as (asti) and after the Aorist character sic ,
As आप एवेदं सालल सवमाः ॥ Here आः is used instead of आसीत्; but also अहरेवासान्न रात्रिः (See Maitr S. I. 5. 12). So also with s-Aorist, as गोभिरक्षाः (Rig IX. 107. 9), प्रत्यञ्चमत्साः (Rig X. 28. 4). And अभैषीर्मा पुत्रक, the आट् is not elided though मा is added 6.4.75. अक्षाः and अत्साः are examples of सिच् without इट्. Compare 8.2.73.
The word आः is the लङ् of अस्, there is added तिप्, then शप् is elided, then स् is changed to रु, and it is turned to visarjaniya. The words अक्षाः and अत्साः are derived from the roots क्षर् (सञ्चलने) and त्सर् (छद्मगतौ), in the Aorist, the तिप् is elided 6.1.68, the सिच् is elided by 8.2.24, and the इ of the roots is changed to visarga. The augment इट् is not added as a Vedic irregularity.,