Impale chance craft not adding to other sources of impale

I've tested on a single mob using southbound gloves and dread banner to count impale procs. Ran a few times over and noted the average results:

20% Impale craft only = can't tell but it does impale by itself at about a 20% rate.
20% from dread banner = 20%
20% Impale craft plus 20% from dread banner = 20% (!)
40% shattering steel + 20% dread banner + 20% master of metal node = 80%
40% shattering steel + 20% dread banner + 20% master of metal node + 20% craft = 80%(!)

I am using a Paradoxica for this.

So basically Sources of Impale seem to stack together ok except for the impale chance+phys craft.

Many thanks.

I don't see any impales happening with just the weapon craft. Running Static Strike - CoC - BV, tested on Kitava since it's easy to see impale stacks there, but I don't see any the entire fight.

No chance to impale on tooltip either.