The excess penetration of western first line APFSDS at the time of the tests was marginal at best...
The M829 only has a perforation of less than 480mm of zero obliquity RHA, because of the tendancy of the failure path to orient itself to the plate normal, the effective penetration is around 300mm of plate at 60 degrees (or the oft-quoted 600mm).
With the T72B, the protection level is so close to this that even an inert plate of the weight of the K5 brick (~35mm steel) is sufficient to offer nearly complete protection while the brick is intact. I am sure that the effectiveness of the K5 blocks exceeds the base armour level of the block, but the exaggerated effectiveness given in the reports is not necessary for the test results to be observed IMO.
I doubt that it is sufficient to immunise even a T72B against the later model APFSDS rounds though - the M829A1 can exceed 600mm of zero obliquity armour, or around a 370mm plate, or 740mm effective perforation.
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