The default values of these attributes are 1587M, which was the maximum memory allowed by Windows when the build was made. The latest security patches have reduced the maximum memory to 1387M. Therefore, for all installs 1387M should be used.
The max_indexer_memory is the memory used allocated by the Enforce Server. Lowering this number helps when indexing with low memory, but it comes at the cost of indexing performance.
The max_loaded_indexer_memory is the memory used by the Monitor. Lowering this number is useful only if you are seeing JVM heap errors. Otherwise, this number should be kept at 1387M.
Splitting an EDM into multiple EDMs does NOT help memory, it makes memory issues worse, because each EDM index has an overhead of 200MB.