I tried what you said and can say, that the FLIRC dongle reliably receives key presses from the Harmony up to 15ft away, when the dongle is connected to my Mac (where I trained it). I even pointed the remote opposite of the dongle and it still received the events.
However, as soon, as I've put it in the Raspberry, reception is sub-par: no further away than 3ft, direct aim needed, very often key presses are missed.
I tried it on two different PIs in order to ensure that it is not a software problem on the Pi I used it until now. One Pi is running MLD (VDR client) the other Raspbmc. Also in Raspbmc I can hardly control the OSD.
Of course, I also browsed the VDR and XBMC forums, but what I've read here is that many other have the problem with the FLIRC dongle as well :-(
I will try to use an USB extension cable tonight to put the dongle directly in front of the TV, but if it still not working as expected I am sorry to say, that I have no use for the FLIRC :( though it is a really neat product