Okay I uploaded the scene file to you guys, It's a client project so it has to stay private.
In the Slate Material Editor you will see that there are 2 Tabs. One for "Street" & another for "Glass". The "Glass" tab has 2 material setups, one with thin, and one without thin Refraction. So you can select the glass object with the labels on them and just apply each material to see the difference. You will see that while using thin refraction on, the glass will get darker. You can compare that to the 2 center glass doors. Also the render time gets shorter of course because of thin refraction on. If you use a CoronaBitmap for the Alpha maps in the Mask Layers for the CoronaLayeredMTL, you will see it doesn't work correctly. Only 3dsmax Bitmap will work right.
Another issue I brought up in another thread that is also in this scene, Is the "CoronaUvwRandomizer". If you have "high quality blending" enabled it more than doubles the render time with only one map. This seams like a bug or can be made much more efficient. You add a few maps in the scene with "CoronaUvwRandomizer" with "high quality blending" enabled and your render times can skyrocket. Please see comparison times below for just one map in this simple scene.
"CoronaUvwRandomizer" with "high quality blending" ON - 3min 55sec
"CoronaUvwRandomizer" with "high quality blending" OFF - 1min 25sec
I uploaded the File using your Dropbox Option cause the .zip file is 512MB. The file is Labled "Don Farese - Test Scene For Corona.zip"