Full disclosure - so my rear window was dark because of the Formula One Stratos tint we added (20%) all around. The 20% on top of the already very dark smoked glass was a horrendous combination and quite frankly unsafe.
I went back to where I had just got my windows tinted, and I had them replace the rear window tint with 70%, which they shockingly did at no charge. Low and behold, we can now see out of the back window perfectly fine. Even with 70% tint, the rear window still looks very dark with low visibility inward due to the smoked glass.
When it was at 20%, in broad daylight, we literally couldn't see people sitting in their vehicles when they were behind us. We could make out certain vehicles and colors, but it was mostly just shapes. Also, we have a white X and at 20%, we could not tell the spoiler was white because it was so dark.
The 20% on the smoked FWD passenger windows is perfectly fine, by the way, with no visibility issues.
Just wanted to give an update on our initial, self imposed, bad visibility experience.