Question about the automatic quality setting in Nero Video 2015

I've just updated to 2015 platinum. I want to make a dvd i using Nero Video, and wonder why the quality automatic so low, that I can have more than 12 hours worth on there?
In Nero 12 4 hours of the same sort of video file filled the disc with a nice result.
How do I make it so that the quality is adapted to the disc size, but not lowered to that level?
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