The currently provided reflection checker is poor in terms of both quality and accuracy. In the two threads linked below there is a discussion about the flaws, plus updated MatCaps to provide the solution. This patch basically does the replacement of the MatCaps, so the change can be easily merged. I have renamed the matcaps too to be more in line with what I see in the repository.
See ends of these threads for reference:
https://devtalk.blender.org/t/call-for-content-matcaps/737/348
https://devtalk.blender.org/t/call-for-content-studio-lights/1869/34
Note that I am just the committer of the patch (to get the topic up to speed before 2.80 is released).** The creator of the MatCaps is HISEROD: https://devtalk.blender.org/u/HISEROD**. He should be mentioned in the commit.