ML700D,
No matter what camera you use, you still have to expose to the right (ETTR) when filming at Dual ISO. Needless to say that you should use Dual ISO only in the high-resolution modes with enough vertical resolution, (the 1x1 or 1x3 crop modes). Activate your Zebras and Histogram, find your brightest spot in your scene, magnify it and start increasing the exposure until zebra stripes start showing up on that spot. Then dial the exposure down by 0 to 1/3 of a stop and watch the histogram. If it shows an exposure reading between 0,1 and 0,3 you should be fine since you will be close to the highest signal-to-noise ratio (SNR) in the darks without blowing up the highlights. Also play around with the Dual ISO numbers. The 100/800 setting provides excellent results when there is enough light. When it is too dark though, then 200/1600 or even 400/3200 may provide better results. In scenes with very high contrast, you may want to increase the second number by one more stop, e.g. 100/1600, 200/3200.
And last but not least - do not try to push the Shadows too much in post! If you do, at a certain point, you will get ugly noise artefacts in the darkest areas. An image with minimum detail in the darks looks much better than one with noisy shadows!
And finally, practice, practice, practice! If you do, you will very soon find out what ML is really up to.