I was under the impression that combat with an SLF did not in any way affect your kill awards, and this may still be the case as my observation is not very scientific.
Twice within the last 24 hours I have been in the Haz-Rez with my conda and an SLF until I ran out of ammunition (about 40 minutes), and also once in my Python and once in my FDL, again each for about 40 minutes until running out of ammunition. In both cases with the Python and the FDL I gained twice as many combat percentages than I did in the conda with the SLF.
Like I said not very scientific. For a start on both occasions in the Python and FDL, my combat percentage rating at the start of the session might have been .9 of a percent, and on starting the session with the conda it might have been at 0.1. I suppose also I should try a session in my conda without my SLF. However like I said at first glance for me, my ranking speed seems to be twice as fast without my SLF, which as far as I know is not the way FD has supposedly designed it. Has anyone else any experience of this?