I had the same issue as you after building NBS.
All is a matter of confiance more than aiming a strict value.
Actually at the national I put a mark on my boat breaker rope under tension. The mark was just outside the last pulley about 1m up the snout.
Everyday I pulled 20 cm further.
At the end of the nat, the mark was 30 cm under the snout
.
Actually the right tension is when I can't pull on my 6:1 purchase anymore (eg we could imagine it is a 300 kg tension).