Perhaps the 161mm @60°/320mm-340mm figures are for protection along the frontal arc of the turret (+30°). This would put the those figures roughly in line (~393mm) with the 400mm cited by the CIA if they were only considering 0° impact obliquity.
This is kind of obvious. I believe there was a underestimation of Soviet KE projectiles by NATO going into the 80's that snared both M1 and Leo 2 protection development. You can see both designs upgrade their inadequate armor through the 80's to compensate for those deficiencies.