Modern Mitchell to 100mm Ball Adapter

I believe this piece is the industry standard, but I just don't understand why they don't design it to tie directly to the mitchell plate. As of now I need to find a large washer to go under the Mitchell plate and above the head's tie-down knob. If it has to be this way they should probably include one with the adapter. If you don't, the knob will only attach to the adapter and slip right through the mitchell plate--so essentially the head and adapter can fall right off of the Mitchell. Not a huge problem to solve, just need to find that large washer. Otherwise machined well.