try to monitor transfer speed using external application such as
http://forum.flashfxp.com/showthread...&threadid=2400
i suspect there is actually no problem in transfer speed, but rather minor issue with graphing module. to draw that graph flashfxp samples it's own speed every few ms, and what happenes is once every "~28sec" graph update and flashfxp's internal update happen at slight offset so flashfxp miss it and it has 1 less sample to base it's graph on.
but then again, i could be wrong...but just to make sure consider monitoring transfer speed using another application.