When running WildFly standalone server as a Windows service, service install registers start command standalone.bat with no option.
By default, standalone.bat loads standalone.conf.bat, and not standalone.conf which is designed to Unix platforms.
It is possible to load a specific standalone.conf.bat file setting environment variable STANDALONE_CONF with its path. There, it is possible to set JAVA_OPTS options but not server options.
To avoid to edit WildFly release standalone.bat file, I recommend to create a copy of bin/service/service.bat as bin/service/service-myproject.bat where you can adapt start parameters and add --server-config:
set STARTPARAM="/c \"set NOPAUSE=Y ^^^&^^^&
    standalone.bat --server-config=standalone-full.xml\""
At the same time, this specific service-myproject.bat allows you to tune your service installation with SHORTNAME, DISPLAYNAME and DESCRIPTION variables.
Do not forget to invoke service-myproject.bat with both /user and /password options so that the service is allowed to cleanly stop your instance with granted administrative user.