To reproduce:
1. Open attached project;
2. Run scene test and select Cube;
3. In lightning >> Baked GI >> Make atlas size 1024;
3. Go to Object window >>Mesh Renderer >> Scale in Lightmap and set to 10.46 ("Object's size in lightmap has reached the max atlas size" message appears);
4. Go back to lightning >> Baked GI >> Make atlas size 4096;
5. Go to Object window >>Mesh Renderer >> Scale in Lightmap and check if message is gone

Expected result: When Atlas size is set to 4096, message should not appear when the scale is the same as for 2048
Actual result: Switching from 2048 to 4096 doesn't affect the warning message, despite the object actually fitting in 2048 atlas size.

Reproduced in: 5.4.4f1; 5.5.2f1; 5.5.2p1; 5.6.0b11; 2017.1.0a2

Fixed in: 2018.1.0a1.