Debatching flat files does not use the Envelope/Document schema model. This is for Xml files only.
To debatch you should just need the Order schema
Order – Postfix, hex 0x0D 0x0A maxOccurs = 1
The flat file disassembler will iterate through the flat file and generate a new message for each Order it finds.
You can send me your schemas and an example document if This does not work.