How does tcksample sample FA?

Dear all,

Could anyone explain how sampling FA via tcksample is comparable to averaging FA within a binary mask of a tract? Tcksample computes FA along each streamline of a tract, but is the FA weighted by any feature such as streamline density?
I am asking because while tcksample gives me left-lateralized FA values of a given tract, averaging FA across tract volume gives me a completely opposite laterality pattern of the same tract. This is the case for some tracts but not all.
Is there any research done on comparing along-tract microstructural analysis to simple volume averaging?

Thank you for any suggestions,

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