Nameless Cults - Crom's Boon


I’m currently enjoying the Nameless Cults. I just read the box about Crom. It reads:

Once per session […] the gamemaster may choose to offer a Cimmerian character an additional 2 Momentum to a single attack, above the normal maximum of 5d20, at the cost of 3 Doom.

What has 2 Momentum to do with the maximum of 5d20? Also, 2 Momentum for 3 Doom seems like a bad deal. I assume this is meant to say “2 additional d20”.

The intent is to be able to add up to 2 more dice beyond the 5 dice threshold.