I have been dialing in espresso with a Vario grinder and wondering why I was getting such wildly inconsistent results. Turns out I mixed up the fine and coarse adjustment levers.
I swapped mine to the steel burrs to help with lighter roasts and longer espresso ratios 1:2.5 - 1:3, so this sounds like the opposite of your experience. Of course the steels also help with v60's down the other end of the macro range. Where is this information coming from, that the ceramics are better for light roasts?
I might have crossed my wires, it was probably just a forum post I misread. I happened to have new ceramic burrs so I went ahead and installed them.
I got closer to a perfect pull this morning after adjusting the right lever! Unfortunately I'm out of that coffee now so the process restarts with the next bag.