Nice work! Essentially, Magic Lantern is able to recover closer to the 'sensor DR' - by mitigating the effects of downstream read noise probably introduced en route to the off-imaging-chip ADC in Canon architectures.
The extra 0.8EV 'highlight headroom' (or sorts) is interesting. Makes me wonder if something similar is going on with the Nikon D810 & the 36MP sensor in there. DxO data suggest they're able to map a higher signal off the imaging chip to the same Raw value at ISO 64 -- essentially like extending the effective full-well capacity of pixels at this ISO.
I guess the concept is that lower ISOs give more detail (bits per stop) in the highlights and higher ISO's more bits per stop in the shadows (sacrificing highlights for more shadow detail). Therefore it would seem correct that at ISO 64 you could extend the DR in the highlight end a bit more than Canon's ISO 100. Your quality of signal would determine what you get in the shadows.
Dual ISO just uses the best of both ISO's beneficial range and leaves the overlapped ranges untouched.
That brings up an interesting point though. Dual-ISO doesn't really yield lower resolution images. Only the highlights and shadows are half resolution and it's difficult to notice that based on how our eyes work. The rest of the image where the high and low ISO overlaps is essentially untouched and full resolution of your primary ISO. The wider the difference in ISO, the less overlap and therefore more potential to have your image de-res'd.
If you are shooting in daylight and want to recover shadows, use a high ISO of say 800 and a recovery ISO of 100. If you are shooting in low light and want to play around with HDR in that realm, you should increase your recovery ISO. I haven't tried low light HDR but it seems conceivable you could get better results than without Dual-ISO. Say using ISO 6400 and a recovery ISO of 800 or 1600. I'll have to play with that and see if there are any real benefits.