In the Old Church Slavonic language (OCS), the little yus Ѧ represented a nasalized front vowel, possibly [ɛ̃], and is traditionally transliterated as <ę>, while the little iotified yus Ѩ, as it is clearly seen from its name, is [j] + Ѧ, that is [jɛ̃], <ję> and is a ligature of I and Ѧ. The little iotified yus Ѩ was written in the beginning of words and after vowels where it was read as [jɛ̃] (e.g. ѩти [jɛ̃ti] “to take”, imperfective), or after consonants where it was read as [ɛ̃] together with showing that the previous consonant is palatal, but in this last case Ѧ was more typical, e.g. възѧти (vъzęti) [vŭzʲɛ̃ti] “to take”, perfective.
As for the OCS word for “five”, it was пѧть (pętь) [pɛ̃tĭ], derived from the Proto-Indo-European *pénkʷe. That word had neither [j] nor palatal [*pʲ] which didn't exist at all in OCS. That is why the spelling пѩть is highly divergent and weird, it can be explained either as a typo or as a highly idiosyncratic local and late variant. Even the modern Russian Church Slavonic has it with Ѧ, cf. Genesis 1:23:
The little iotified yus Ѩ is not typical after consonants.