The preview width and height parameters are always in the camera config file, so if you added them, they are duplicates (and will be ignored).
Please read through this thread as it has pretty detailed explanation how to configure the correct tof sensor (old or new) for a custom configuration.
Camera-server-config-helper is indeed helpful. If you use it correctly, you should not have to manually modify the resolution in the config file.
If you still cannot get this to work, please let me know what cameras you have plugged in (and which camera ports) on your voxl 2 mini.
Alex