It tested it now for quite a while and always the Pyroblast proc were subpar.
With many thousand Fireball casts and a Crit rate above 50%, for the ease of calculation lets say 50%.
With improved hot streak you should roughly have 25% to double crit. Sometimes more sometimes less. If you add the proc from a “normal” hot streak, it should be even higher.
After a lot of time and testing it’s always been below 20%. Still this may be bad luck, but I wonder if someone else also recognised something similar?
And before you ask, my Crit chance is closer to 60% than 50% and still proc below 20%
And it’s been tested only with fireball and scorch.