You are correct.The faster you run a diver the deeper they go.That would include a crankbait.A weight does the opposite and raises higher faster you go.Those Smithwick perfect ten (P10) cranks produce well especially when the water is at its coldest.Like now.They run the shallowest and have a more subtle action.Most guys add a 1or 2oz sinker to the P10 but clip them in the middle of the lead.Like 20/20 to 30/30.That means 30ft then clip weight then 30ft more then put on board.If you have the weight clipped or tied inline just 6ft from lure you are netting fish with weight attached to line.Most guys clip weight 20ft or more from lure so can remove weight before they can see or net fish.You will have to look at dive curve to see how deep your lure is running.When you add weight that complicates the depth you are trying to achieve.You can usually add 4ft of extra depth per ounce of weight.But when running really slow,like around 1mph,that depth with weight goes even deeper and can be difficult to predict.Also with this really cold water and slow trolling speeds,causes a lot more missed fish.Pullbacks with no hookups.That's due to lathergic fish and hooks not penetrating at slow speed.