The short is substituted for the vowel of the aṅga (stem) i (eti) before the augment yās in the Benedictive, when a preposition precedes it.,
As उदियात्, समियात्, अन्वियात् ॥ This is an exception to the following sutra by which a long would have been substituted. But ईयात् without a Preposition. The अण् 7.4.13 is understood here also. Therefore ए form of इ will not be shortened, as आ + इयात् = एयात्, समेयात् ॥,