One thing that keeps biting me in the trnasition from Magento 1 to Magento 2 is that sometimes the etc
folder has an area hierarchy.
For example, in Magento 1, you system configuration file (respoisble for building out a module’s configuratioin UI) lived in
etc/system.xml
In Magento 2 this file lives in
etc/adminhtml/system.xml
Magento 2’s way make more sense (and reflects that the “area” system is well thought out), but it takes a little getting used to. If you’re not seeing the configuration changes, check to make sure your file’s in the right spot.