Because dynamic range is the difference between EIN and input clipping level, maximum dynamic range into a recorder will be achieved when using minimal input gain, essentially line-in at "unity gain", although the concept of unity gain doesn't apply directly to a device where the output is a recorded file. Unity gain means the level of the output signal is equal to the level of the input signal.
The test above is the opposite of that. Essentially indicating the worst possible dynamic range achievable through each recorder, very much dependent on how much gain is available.