Sorc masteries and fire damage.

[RogueMage]

Brista, your example is correct except for the details on Crushing Blow. CB can be triggered on each hit, and the game treats Ex Arrows as two separate hits: one for the fire splash, and a second hit for the arrow itself. As a result, monster B takes two hits, each of which has 25% chance of Crushing Blow.

Note however, that CB damage on ranged weapons is half that of melee weapons. Spirea has a good summary of CB damage here:

Crushing Blow Damage Calculator