In how/ on how

Hello,

I understand that when using the verb " to play" in combination with the word "role", the preposition "in" has to be used as well, as in: Fungi play an important role in recycling organic matter on the forest floor.

However, I wonder if the use of "in how" versus "on how" is the correct form when used with verb and word mentioned above, just like in: The cornea plays an important role in / on how light is focused on the retina.

My intuition tells me that it should be in how, but on how, on the other hand, seems to be more often used in other constructions.

Thanks in advance.