FI does not depend on the numer of steps that were needed to find the target. So, the FI would be the FI of ubiquitin, either it was found in 1 step or in 1 billion steps.
Of course, it is 1 billion times more likely to find the target in 1 billion steps then in 1 step.
You must not confound the FI with the probabilistic resources of the system. They are both important, but they are two different things.