[Ifeffit] What differences are there between Athena and AUTOBK backgrounds?

Hi all, Today I tried making Athena perform exactly the same background subtraction as AUTOBK 2.61 (all parameters the same, working on the same data, using the same theoretical standard, etc.). I then let FEFFIT take the chi(k) data for each and perform a Fourier transform. When I did this, AUTOBK would always generate a very low r (< 0.2 angstroms) peak of significant amplitude that was nearly absent in the Athena background. There were other subtle differences as well, but that one stood out. Of course, a peak that low in r should have no effect on the fit, but it made me curious--were substantive changes in the background subtraction algorithm made when AUTOBK was incorporated into IFEFFIT? --Scott Calvin Sarah Lawrence College