This is very tricky. What do we have in stop short of? Is it 1) as Jim suggests, a particle phrasal verb (stop short) plus an optional PP with of as its complement? 2) an ordinary stop with a PP headed by short of as a secondary subject-oriented complement? or 3) a particle-preposition phrasal verb like put up with? None of these standard tests yields entirely felicitous results:
1a. ? It was of counting his chickens that he stopped short.
2a. ? It was short of counting his chickens that he stopped.
3a. ? It was counting his chickens that he stopped short of.
1b. ? Of counting his chickens was where he stopped short.
2b. ? Short of counting his chickens was where he stopped.
3b. ? Counting his chickens was what he stopped short of.
But the idiom stop short does not ordinarily mean stop before reaching a point, but stop abruptly.
On the other hand, we do have the idiom fall short, meaning fail to reach a given goal.
And That is a point short of which I will stop is not nearly so absurd as Churchill's That is an impertinence up with which I will not put.
So on balance I’m inclined to understand short of here as a compound pronoun (with short in fall short as its intransitive variant). If I’m right, then you’re justified in understanding short of X as a locative prepositional phrase which is dependent on stop and signifies the final location of the subject.