In general, the first component is at the fundamental frequency. But if the number of components is chosen to high (or the db threshold too low) noise can produce a peak at a lower frequency.
Since small changes in the parameters can affect the outcome, I would advise to use the Analysis Wizard for Harmonic Estimation. Here one can easily change settings with a direct feedback on the results. Some background information is also available in the Online Help in the section Tutorials > Data Analysis > Harmonic Estimation Tutorial. The analysis object created can be changed into a formula and used as a starting point.
