Never heard of this law of contonation before, which explains why you can’t ever have a circumflex on the antepenultimate syllable or have it on the penultimate syllable if the ultima is long.
The law is that there can’t be more than one mora between the end of a word and the contonation, a short syllable being one mora and a long syllable being two.
See video.
.i`` * ^ / . . . . . ` `~ 