I believe here is a misinterpretation of the functionality.
The wildcard is used to avoid that earlier content gets overwritten, it separates the files and keeps it individual.
if you do not use a wildcard, then SAP deletes the old content with the same name completely before writing new content to the .read and .conv files
with the wild card you create individual .read and .conv files, and finally an indivdual batch input.
if you want one huge batch input, then you have to merge your source files into one