Stealing requirements: for "called insurance," game theory, or both?

[spentrent]

Some players might decide before the game that when it's time to steal, they'll steal with range X.

Does "range X" add a hard-to-percieve amount of frequency to the hands you'd raise anyway, R, such that (R+X)/R is bigger than 1 but not too close to 2?

Or is range X decided upon because of the insurance it offers if called? For instance KQ called by AT.