Picked up a Frozen Ire, tried it out with my frozen orb since it sounds like they’d work well together but…
Frozen orb hits the training dummy at least 20 times per cast with all the shrapnel, but tundra nova only shows up one time per 3-5 casts of the orb on average.
At 15% chance to trigger on cold skill hit with only 20 hits:
"Probability of event A NOT occuring = (1 - 0.15)20 = 0.038"
There’s less than a 4% chance for tundra nova to not proc on any given cast of frozen orb passing through a target.
Is shrapnel from the skill maybe not counting as as cold skill hits?
Using Ice Barrage gives expected results for tundra nova triggers, so it seems like it’s just frozen orb.