At present for Ecowitt stations, Cumulus uses what Ecowitt deems to be the primary sensors for Temp/Humidity, Rain, Wind and Solar.
Additional sensors are logged as Extra sensors. The data is available on the dashboard, and a revised version of the default web site (available soon) will also display them. Of course the data is also available via the web tags and local API.
For now you cannot map Ecowitt additional sensors into the primary roles.