Well, the tenor part moves according to the needs of harmony but that cutting “bell” tone is produced when the tenor is a fifth above the lead. It's like the fiddle playing the open E string against the melody note on the open A string. If you listen closely to bluegrass duets, you'll find the vocal harmony is often patterned after the bluesy sliding doubble stops played on the fiddle.

And of course the baritone part is sung below the lead, I only meant that the lead singer is usually a high baritone voice so the tenor often has to use a falsetto to get up to the required range.

      - Mark