First of all, I would like to explain more about maxFragmentSize in UPA.
maxFragmentSize defines the maximum size buffer that will be written to the network. If a larger buffer is required, the RSSL Transport will internally fragment the larger buffer into smaller maxFragmentSize buffers. This is different from application-level message fragmentation done via the Message Package. Moreover, any guaranteed, shared, or input buffers created will use this size.
Setting this value to this high value means you can send a large buffer without fragmentation at transport level. However, the application will reserve a lot of memory for guaranteed, shared, or input and output buffers.
The default value of maxFramentSize is 6144 bytes and the maximum size is 65535 bytes.
Please explain more why you need to set this value to 65535 and what the size of each message is sent by the application.