I am working on replicating the sound of Jerry Garcia's guitar using the methods described in Thor Zollinger's excellent instructions. I got to a point where I needed a modulator running at 1/3 the frequency of the carrier. But Montage FM-X operators only go down to a ratio of 1/2 (0.5). I figured out a way to get the ratio I need.
I set Note Shift of my Part to -24, which is two octaves down. Two octaves down is 1/4 of the frequency. Then I set the ratio of my carrier to 4.0. That brought my carrier back up to the same it would have been if I had a Note Shift of 0 and a carrier ratio of 1.0. So far, I was just back to where I started from. But now, if I set a modulator to ratio 0.5, that modulator's frequency will be 1/8 of the carrier's frequency. I can set any ratio from 1/8 (0.125) on up.
What I needed was to get a modulator with an actual ratio of 1/3, I set things up as described above and then set the modulator's ratio to 1.33 using its Coarse and Fine settings. 1.33 equals 4/3. 4/3 x 1/4 equals 1/3, the ratio I needed.
So far, I've mainly been making science fiction/theremin noises, to the great amusement of my wife. But hopefully I'm going to get to the point where it sounds more like Jerry's guitar.
I hope this will be useful to other folks. It was fun to figure out. The Montage is an absolutely amazing piece of equipment.