It varies, if you look at meteor lake [1] the different die go from 27..100 sq mm

(Compared to the h200 which is an insane 814 sqmm)

But I don't see any obvious advantage to small triangular die. Once the die are small if doesn't make much difference vs rectangular as to how many you can pack into a circle (for a given die area), and rectangle are much more convenient

[1] https://en.m.wikipedia.org/wiki/Meteor_Lake