You could try splitting this into 3 schemas.
The first schema is <Root><Any> and will be an envelope with the body xpath set to <Root>.
Then define separate <Request> and <Response> schemas, promoting the appropriate correlation property.
Use the XmlDisassembler and Xml Assembler, specifying the envelope schema.
On incoming messages the disassembler will strip the <Root> from the message, promote the correlation property before passing just the message.
On outgoing the assembler will add the <Root> node and demote the correlation property.