[RobW]

The text says this is weighted towards critical failures on very hard tasks.
But that is a misleading understatement...

A 6d roll is the norm for attacks against a defending weapons master.
for 6 dice: 14 and below = success; 24 and up = failure
According to anydice.com, critical failure is therefore expected 28% of the time.

for 8 dice: 20 and below = success; 28 and up = failure.
And according to anydice.com, 28 and up should occur 54% of the time. That seems harsh.