In bluegrass and country music, there is a common convention for harmony vocal parts. (I believe other styles, such as barbershop, use a similar convention, but I’m less familiar with those.) The most common parts are “tenor” (commonly a third above the melody, thus ending on an E note over a melody in C that resolves to the tonic), “baritone” (a fifth below the melody, ending in a G note in C), and “bass” (which generally follows the chord structure rather than the melody).
These do not necessarily correspond to classical tenor, baritone, or bass ranges. Baritone parts may be sung in the tenor range; tenor parts may be in falsetto (when sung by a man) or alto (by a woman). In fact in an all-woman vocal arrangement even the baritone part might be in the alto range.
Less common, but still widely used, are “high baritone” and “low tenor”, referring to the same harmonic relationships moved up or down an octave, so a high baritone part in the key of C would end on a G note above the melody C and tenor E.
It would be great to have a structured way to represent this in MB. I am reluctant to use the existing tenor/baritone/bass designations as I see those as representing the classical ranges. Also, they are grouped under “lead vocals” in the relationship editor.
One option would be a new “harmony vocals” option with “tenor harmony vocals”, “baritone harmony vocals”, “bass harmony vocals”, “high baritone harmony vocals”, “low tenor harmony vocals” as sub-options. (If there are similarly structured parts in other genres they could be added to that list.)