It seems like IRISMAN coverflow UI zooms and/or crops the game covers saved in the cover folder even though they are actually at the correct size. I have noticed this buggy behavior with covers both at 260x300 or 520x600 pixels. I personally use 520x600 pixels as PS3 cover size since I find 260x300 pixels to be too blurry at 1080p. But even so, the cover size should be perfectly downscaled to 260x300 pixels while retaining more details. Instead, IRISMAN adds some processing that seems to zoom in the image and wrongly crop it as well to fit the coverflow placeholder.

I haven't tried with PSX, PS2 or PSP games though. Only PS3 but I would probably think that the behavior is the same with these covers too.