This is an open bottomed octagon ring that gets cemented into the building floor (deck) after being nailed to the wood sub flooring. By using back plates and covers, it becomes a complete deck box and is available in depths from 2" to 6" with knockouts from 1/2" to 1". It is called a concrete ring when it is extending an existing mud box and it can be called a mud box when it has a back plate and serves as a mud box. A classic mud box, however, comes as one unit with the back plate welded in place.
Those boxes are too far back. You'll need to use some goof rings.