This seems to go against the line of thinking that associates bigger pixels with more DR.
Well, such thinking was always wrong to begin with, but anyways...
Forget about DR. All cameras today are going to have nearly 12 stops of DR at the very least, so it's pretty meaningless now. In today's cameras, DR is a result of processing decisions more than anything else. The reason this is so is that DR is limited by the bit resolution of the camera's ADC. If you could measure the analog DR of the sensor, it would likely be larger than what DxOMark is reporting. This is why a Canon Powershot S100 can have nearly as much DR as a Canon 5DMIII.
The measure you really want is SNR. Look at the SNR and there's a huge difference between the two cameras. The SNR tells the real story (which is, in this example, that the 5DMIII has about 3.5 stops less noise than the S100.)