Does the local memory usage increase with banking and coalescing?

Actually I am not sure if the compiler configures the Block RAMs with a width of 32 bits or 40 bits. Either way, you should also take the size of the buffer into account (the size itself might require more Block RAMs than the minimum number that is needed to provide the necessary number of ports for all accesses). Moreover, the type of accesses also matter. Writes need to be connected to all buffer replicas, while reads need to be connected to one. with double-pumping you effectively get 4 ports per Block RAM. e.g, for 5 reads and 1 write, you need 2 Block RAMs per every 32-bit (or 40-bit) bank width, but for 5 reads and 2 writes you will need 3. To be honest, accurate prediction of Block RAM usage is not very straightforward.