Originally Posted by TooManyShots
Incident is light falling on the subject; reflective is light coming off the subject viewed by the meter/camera. This is chiefly why incident is reliable for nailing some (but not a lot) of exposures, with the only other refinement being multi-spot metering.
I would view your 30d metering as potentially very misleading with a 1 stop difference comparison and urge you to concentrate on using incident metering with aim-back to camera from subject. It's not perfect but will eliminate the margin of error caused by an evaluative metering system that is averaging the luminance of several small areas of reflected subject light.