Steps to reproduce:
1. Download repro.zip and open "TestScene" scene
2. Set "R" in TestOverlap.cs to 0.7 and start the game
3. Console will return True value
4. Set "R" to 0.25 Console will return False

Expected results:
In both cases returned value should be true
Actual results:
Physics.CheckSphere returns false value when Sphere is small enough to fit inside non-convex mesh collider.
Works fine with Convex Mesh Collider, Sphere collider, Box Collider.

Reproduced with:
5.2.4f1
5.3.6p3
5.4.3p2
5.5.0f3
5.6.0a3