C
Concrete guy
12mm is good for stone but most porcelains will be 9mm/10mm , so seen as most stone is machine cut and they will mitre on the same machine then maybe go the porcelain thickness route.. unless it can be there can be a removable part to allow for 12mm to 10mm
As this is a back cut, (the cut edge won't be seen) a 12mm cutter would just overlap the bottom edge of the tile. I see 12mm as more versatile?