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sigma fitgauss question

I am using the centwave algorithm for peak detection, selecting the 'fitgauss=TRUE' option.  I am curious to know how best to interpret the values output by fitgauss - in particular sigma.  In the centwave algorithm, there is an parameter specifying the min and max peak width, in seconds - I usually use something like c(2:20) for UPLC.  When I look at the gaussian sigma values returned, it has raised two questions for me:

1. why are there peaks in the resultant xcms dataset for which the sigma values is larger - sometimes by an order of magnitude - than the max peakwidth setting?
2. how do I interpret sigma values of 'NA'. 

I am guessing that the answer to the latter question is that the gaussian fit is bad, and no mu/sigma/h can be returned. Any insight is appreciated.

Corey