You may have tried this by now... I'm not sure if recalibrating the display digitizer even affects the silkscreen or stamp area, and you seem to have said you haven't noticed a problem, but try it anyway.
FitalyStamp includes "adjust position" which you should be able to use to set up your stamp. FitalySetup includes a "sure mode" to improve FitalyStamp accuracy (but slow it down), and a digitizer test.
I found an online discussion of apparently incurable, but manageable misreading of the silkscreen on some Handspring 180g, not in the context of Fitaly, which apparently showed up as the buttons not working and Graffiti written close to the letter/number split coming out as the wrong kind of symbol.