Spring relocation box position

The spring relocation boxes are wider than the frame by a 1/2" or so each side. Im thinking they are to be installed centered under each frame rail about a 1/4 over hanging the frame on each side that would make them about 35-3/4" center to center between them just like the frame rails. Does that sound right?

I have seen them mounted more towards the center of the car and flush with the frame rail in the inner fender area of the car. Seems to me that would throw off your center to center measurement and not placing the springs centered directly under the frame. Any comments or suggestions before I take on the project?

Thanks