I just happened to come across this on blendswap, which then pointed me to a youtube video that shows how to set up a node group that gives you some much easier (and probably more realistic) control over fresnel reflections, taking roughness and minimum reflectance into account :)
The author of the video didn’t provide a link to download the node group, so I figured I’d copy his setup and upload it here.
Download node group
Licence: CC0