HI @Motive_Zine, correct, there’s no ability modifier for Invoke, but there is this clause in the description of favor:
When you make any move roll that falls within a domain of your deity, you may spend favor before you roll the dice to increase the result by +1 for each point of favor spent.
So Clerics will typically spend favor to counteract hubris when Invoking.
Hubris is obviously pretty subjective, but when I’m assigning it a value I enjoy putting myself in the role of the Cleric’s deity. How much of my power are they requesting, and to what degree does this invocation further my cause? I consider these things in balance and try to arrive at what feels like a fair number between 0 (trivial) to 6 (miraculous). The mechanics are purposely more vague than, say, the Magic-User’s spellcasting because I wanted the Cleric player to feel like they were petitioning a higher power (their deity, but also the Judge).
The best but perhaps unsatisfying answer is that you’ll need to get a feel for it at your own table, and that might take a few tries. It’s okay to get it “wrong” and adjust, because who among us can reckon with the whims of the gods?