More loop volume means more oxygen in the loop, means less variation in percentage, if you work harder for a short while.
Propably more a theoretical issue though.
I personally prefer the OP valve set to low volume. Dont like too much resistance on exhalation. Nor the added weight.
I dive my Atlantis 6 clicks back from fully closed, but valves vary, so try for yourself. Mine wents on each exhalation.
To my knowledge Dolphins has less number of clicks.
I know some people will disaggree, prefering fully closed, and only venting once in a while, but i guess you already read through previous posts
.
Best regards
Bo