Steps to reproduce:
1. Open Unity
2. Right click in project window
3. Create a few basic sprites - triangle, hexagon etc.
4. In the Project view use the icon size slider to make the icons bigger and smaller
5. When in their smallest possible mode, the preview defaults to the base sprite which is a square.

Expected: The sprite preview lets you know quickly what sprites look like
Actual: When the icon view is smallest, they all become the same, until taken to the scene view, making it hard to understand at a quick glance what sprites are what

Reproduced on: 2017.2.0b2, 2017.1.0f2, 5.6.2p2, 5.5.4p1