I have a question for the vaiyākaraṇas among us (who may find it very basic, in which case I apologize in advance):

In the Tājikayogasudhānidhi of Yādavasūri (fl. possibly early 17th century, possibly in or near Gujarat) there occurs the following stanza (12.15), the form of which is corroborated by several independent witnesses:

janmalagnapatir uttamavīryo yadgṛhe januṣi tatra ca dṛṣṭe |
tena vā sahita asya ca labdhis tad yathāṅgasukham abdatanau syāt ||

(As the meaning is quite technical, I give my translation: 'If the house in which the ruler of the ascendant of the nativity is [placed] with excellent strength in the nativity is aspected or joined by that [ruler, there is] attainment of [the matter signified by] that [house]: for example, [if it is placed] in the ascendant of the year, there will be pleasures of the body.')

From the context, the underlined phrase clearly stands for sahite + asya, with e > a. While this is standard sandhi before other vowels, I have never come across it before a. Is there a traditional rule that allows for  this?

Best wishes,
Martin Gansten