My installation of WeeWX is on Debian and from the .deb package. My path configuration is the default from the package installation:
# Root directory of the weewx data file hierarchy for this station.
WEEWX_ROOT = /
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.
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[StdReport]
# This section specifies what reports, using which skins, to generate.
# Where the skins reside, relative to WEEWX_ROOT:
SKIN_ROOT = /etc/weewx/skins
# Where the generated reports should go, relative to WEEWX_ROOT:
HTML_ROOT = /var/www/weewx
As you can see, with WEEWX_ROOT set to '/' the other variables simply specify the entire path which kind of makes WEEWX_ROOT meaningless here. On Debian the default HTML directory is under /var/www which is at variance with other distributions.