[tyw]

it should be roughly equivalent to knowing the salt of the hash you're attempting to crack, right?

[drcode]

"Next, I set my 1Password master to a combination of two passwords. "

OP made it clear one of the two items being combined is "short" and hence if the other item is known it would be much easier to brute force.

(In your lingo, it would be like knowing the password and then having to derive the salt, which is easy with a small salt.)