Would there really be more VLS cells than the Sovremenny MLUs? The Sovs are already larger than the Type 52Bs yet only fitted 32 AJK-16s. Does the 52B have more internal space to fit the extra VLS cells?
I suspect the ship is weighted in such a way that you need to keep its balance by having a VLS on the rear. The original configuration for the 052B is one arm based missile launcher in the front, and in the back. But each of these missile cache contains 24 missiles each. You can't put all the missiles in the front after renovation as it would unbalance the ship. So you need to put at least some missiles in the rear. The ship's configuration could be 32 missiles in the front plus 16 missiles in the rear with the VLS or 16 here 16 there. Its either that you have to find some other way to counterbalance the ship and put some weight in the rear.
The Sovremenny itself is designed in a different era. Space wise it isn't as efficient, and its primarily designed for those eight huge Moskit missiles. Like the 051B, the 052B might have been designed for future VLS usage in mind but the VLS systems were not available during its time of construction.