Aha... blast wave mentions a knockback:



A wave of flame radiates outward from the caster, damaging all enemies caught within the blast for 462 to 544 Fire damage, knocking them back and Dazing them for 6 sec.



I may have confused the two, I guess.



Anyway, I was wondering if I fire off 4 blast waves simultaneously, will the effected characters only be knocked back the initial value, or is there any stacking involved.