Cary 630 FT-IR Library matching algorithm

I have recently ran two standards on the Cary 630 FT-IR  using the ATR module - qualitative search.  One is Heptanes and the other is N-Heptane. 

I then ran four samples -  three were N-Heptane, the other was Heptanes and compared them to the two standards in my library. 

The results:

The Heptanes sample gave a 95% match to the N-Heptane standard and only an 88% match to the Heptanes standard.  The spectra's look different - extra peak at 700wn/ Intensity of peaks etc. The solvents are not the same - this result would have passed specifications however it should have failed!

Does anyone use the library matching algorithm as part of routine analysis and have any information on how to avoid false positives/ false negatives ?

Is the search algorithm reliable / capable?

Is ATR module appropriate for the analysis of liquids? 

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