deriv LSK ETT STT aSTA ALPH OLDHOMEPAGE NEWHOMEPAGE
Rule kupvoKkaFpauca says that you may freely choose —
azvaFpazyati अश्व⩆पश्यति
kSiraKkAGkSati क्षिर⩆काङ्क्षति
or
azvaHpazyati अश्वःपश्यति
kSiraHkAGkSati क्षिरःकाङ्क्षति.
Yet, you'll never see the spellings Fp ⩆प् Kk ⩆क् in print anywhere outside grammars. Even people who say Fp ⩆प् Kk ⩆क् spell Hp ःप् Kh ⩆ह्. There is little need to have letters for those sounds because they are free variants — you spell azvaHpazyati अश्वःपश्यति and the reader chooses reading that aloud as azvaHpazyati अश्वःपश्यति or azvaFpazyati अश्व⩆पश्यति, same meaning always.
There are not even symbols for K ⩆ F ⩆ in UNICODE. Instead, I'm using Union Above Intersection U2A46.