I have been asked to build a Mission Style Bed for a friend. It will be a twin with box spring. the wood will be QSWO where required for the appropriate look. The finish will be traditionally dark. the question is this...What is the appropriate top rail (above the slats) width? I have drawn several virtual models and a width equal to the narrowest width of the arched bottom rail looks best on the screen. However I think that this may be too heavy in real life. The shown width is 4 inches in the pictures. The bottom rail is 6 inches width with a narrow section width of 4 inches.