Zona, the ti boom insertion depth is similar to a seatpost in terms of how much needs to be below the clamp "line". The boom itself was not marked w/ a safety line so I called and inquired.
There are numerous boom gauges so it can be tailored to stoker weight. We went with the thinnest gauge due to my tiny 5'2" 105lb stoker and we're not experiencing any undo "boing" at all even at high revs.
We're both climbers, she's an outstanding masters runner whose best races are hilly, challenging courses and my best cycling events always have been those with considerable climbing. We're finding climbing to be much easier and more efficient on this new bike.
We live at the base of the Oregon Coast Range mountains west of Portland so every ride for us is a hilly affair.
KRhea