BANA 7.6 says an "exterior" box line should use dot-1-2-3-4-5-6. Attached example shows that it is not possible to use a BRF "=" in a configuration file to achieve this.
Use
file2brl -f minimal.cfg source.html
Error message is
minimal.cfg:7: column 2 is required
minimal.cfg:8: column 2 is required
minimal.cfg:7: column 2 is required
minimal.cfg:8: column 2 is required
exterior-box-line.zip