Hey Nate, and welcome 
I moved your post to Beyond the Manual because that’s the only place we’re allowed to discuss non-PG settings.
I used 650/65/225lpi on 230gsm Pergamenata - which is a paper that is very similar in weight to vellum and it engraved all the way through. My suggestion would be probably 650/25/225lpi to start, and use the Convert to Dots/Pattern setting so it’s not trying to dig deeply.