Praudhamanorama p58

p58

With the intention that here "one for the preceding and the following" continues and that [the application is] respective, he says: "like the end of the preceding". This sūtra has indeed served its purpose by the sūtra regarding that which is treated like the original [sthānivad ādeśo 'nalvidhau, 1.1.56]. Nor should one be under the delusion that this is for the purpose of a rule conditioned by a phoneme, because this too is not intended in a rule conditioned by a phoneme. Otherwise, in ayaje indram, there would be the undesirable consequence of a homogeneous long vowel. And likewise the vārttika: "Or not, because there is an extended application of non-identical nature."
[Pā. sū. 8.3.15] "A visarga comes in place of [r] before a consonant of the khar pratyāhāra and in pause."