Off hand, I'd say keep the line tie in the nose of the bait, tight to where the lip exits the bait, and run the lip at a 45 degree angle to the centerline of the bait. A flatter angle will cause the bait to run deeper, but you may have to put the line tie into the lip a little.
Think of a RC 2.5, and you'll have a good jumping off point for a crank that size.
You can also take a look a one of the Rapala DT (dives to) series that gets down to the depth you want, and see how it's lipped and where the line tie is located.
Every crank has a slightly different shape, buoyancy and center of gravity, so you'll probably still have to play around some.
Also, the shape of the lip also bears on how deep it goes, and how stable it is, too.
If it were easy, I'd do it!