In game the STRV 122 series of tanks reportedly have 600mm of NERA armor surrounding the breech block and including the composite screen of 80mm should have an armor value around 680mm. However when looking into the projection map of 3BM60, the NERA armor around the breech block dead center only has 480mm of effective thickness.
different types of APFSDS affect the effective NERA values.
Composite NERA is not the same as RHA dude it’s not made of entirely of steel y’know so the effective thickness values for RHA are lower because they provide less armor proportionally to RHA