Do you use the sketch layer as a base and build off of it, or do you use it for tone over a color layer?
Sketch goes on top in begining then under after shape is there. Then I duplicate the sketch as a multiply and blur it sometimes and put it on top of everything at about 30 -40%.
Good policy with your drawing style. You might want to consider using the grisaille method of painting/heavily sketching in monochrome to establish tone first, then overlaying that with your color instead. Instead of the traditional way's drawback of obscuring your original sketch, this can often accentuate it and create a much stronger chiaroscuro (and it also tends to preserve the hatching style that is unique to one's drawing).