When using closed dies it is critical to keep the two halves in proper registration to produce a consistent forged object. There is little tolerance for side-to-side or front-to-back migration.
One way to assure this indexing is to make the blank blocks from different size masses. Usually this means making the bottom blank mass larger than the top blank mass so the top will sink into the bottom and create a obligatory fit. An alternative is to weld a perimeter, sort of a corral, to force the registration.
The image “Improving the die mating” attempts to show how theoretically this could be accomplished.
The left image approximates the crudely assembled example shown in the Tiny Acorn Die post. The second image shows how attaching the sacrificial connectors with an outward budge assures they will collapse without being trapped between the two die blocks. The next figure shows that by narrowing the top block it will sink into the bottom block when collapsed and provide a secure front-to-back registration cavity. The right figure shows that by further reducing the size of the top block the resulting indexing cavity captures the entire perimeter of the top block.
In the two right hand drawings the front edge of the top and bottom die halves are not aligned vertically. After the pair is collapsed to form the object cavity, additional metal removal from the bottom block is required to create an in-feed channel for the billet stock.