I am sure that others will chime in on this. From my understanding the method of metering with reflective meters and incident meters differs markedly.
To begin...an incident meter is designed to arrive at an average exposure based upon orienting the incident dome in such a way that the light striking it is akin to the light that is striking the object or scene being photographed. In other words the incident dome is pointed from the object being photographed back toward the camera. In reflective metering the meter is pointed from the camera toward the object being photographed.
To arrive at the scene brightness ration two incident readings are taken. One for a highlight value and one for a shadow value. Then the EV of low reading is subtracted from the EV of the high value. This is how one arrives at a SBR value. A normal SBR would be a value of seven.