Unfortunately diatonic is not the same as triad centered voicing. Triad centered voicing switches the harmonies depending on the note played. It’s so musical sounding you honestly wouldn’t believe it.
Here’s the manual:
https://www.manualslib.com/manual/380763/Digitech-Harmonyman.html?page=18#manual
And the shifting tables for C Maj and Amin
https://www.manualslib.com/manual/380763/Digitech-Harmonyman.html?page=21#manual
Here’s an example of it being used in a recording:
I’m almost positive it would be a simple algorithm to recreate for Eventide’s developers. Just apply the business logic to the Diatonic algorithm for an easy win!