This is yet another microcosm of Ottawa's season, as Cowen played probably his best game of the year. His reward for that improvement is a punishment, and he'll miss two games. Trying to build on an improvement? Not this year, suckers!
Beyond the continued silliness of "improper angles," there's not much room for argument here. As Elliotte Friedmann pointed out earlier this year, rule 48.1 now reads:
"a hit resulting in contact with an opponent's head where the head was the main point of contact and such contact to the head was avoidable [is illegal.]"
Cowen indisputably hits Girgensons in the head--and only the head--and you can't do that, so he's going to sit for two games and feel shame.