Could you check this over
Fragment of a discussion from User talk:Rua
For me, the simplest explanation for the Greek form is just as an athematic -mn̥t-. Greek regularly loses final -t, so in the nominative the result would be -mn̥t > -mat > -ma or -mn̥t > -mn̥ > -ma (both orders are possible and give the same result). In the other forms, the -t- was not final, so it was retained. I see no reason to involve suppletion, unless I am missing something.