@TomG:
It depends. When you assign a physical rendersize + DPI within Cinema 4D, the resulting render resolution is indeed DPI-dependent.
If TR assumes default 72dpi when a physical measurement is set, the render resolution becomes wrong.
However, this needs further information.
Like:
Is he using physical measurement in output?
Does this also apply to Standard-Renderer?
Does this only occur with TR?
But honestly, this smells more like a C4D-bug.