Dev notes:
https://docs.unity3d.com/ScriptReference/Physics.SphereCast.html:

Notes: SphereCast will not detect colliders for which the sphere overlaps the collider. Passing a zero radius results in undefined output and doesn't always behave the same as Physics.Raycast.

Any shape casts with zero radius/size are very likely to produce undefined results. It's better to just use normal Raycasts in those situations.

Steps to reproduce:
1. Download and open the latest attached project("Repro.zip")
2. Move the "RaycastHelper" gameobject around the scene to hit objects at an angle

Expected result: hit.point is always where the Raycast hits
Actual result: hit.point is often reported at the start of the Raycast or behind the actual hit

Reproduced on 2017.1.3p1, 2017.2.2f1, 2017.3.1p2, 2018.1.0b9, 2018.2.0a1

Notes:
- This happens with every shape collider, with radius needed to be set to 0 for the bug to occur
- The project provides a visualization of where the hit occurs, placing a debug display at that point