Closer to centerline is better. If you are using individual weights, I'd keep them over the trucks as much as possible. That will minimize sagging in the center. Watch out for Weaver 4 bay hoppers and other long cars. I typically use bar stock in these with oversize holes for installing the trucks. Then one or two small holes in the centerline that match up with the gaps between the hopper bays. Put small screws and nuts through them to hold the bar in place.
Chris
LVHR
