I have the same i1iSis.
Canson rag 310gsm is right at .45mm. While it works, I have to push the paper and keep a bit of force on it until the feeder grabs the paper.
The main problem I have with that paper (and the 210 gsm to a lesser extent) is that matte black ink, even well dried, leaves roller tracks. I have to adjust the patch width and offset so the tracks run through the patch edges. Then, after finishing, I run a few blank papers to clean the rollers so they don't leave tracks on whatever I scan next.