I had my car tinted last week with Xpel Prime XR+ in pretty much the same darkness. I did 70% on the windshield, all of the back windows & rear hatch, 20% on the sunroof, and 30% on the front doors.
The 20% roof tint makes the interior pretty dark, especially with black interior, and it makes the factory tint even darker looking. It also makes the 30% front windows look like 20% without tinting the sunroof. In retrospect, I may have gone with 35% for the sunroof to let a little bit more light in, but I don't mind the darkness and it definitely keeps the car cool. Drove it around the 100+ degree So Cal weather this weekend and even had it parked at the rooftop mall parking lot where it was 98 degrees for a couple of hours. Turned the AC on for like 5 min during our walk back to the car, and it was completely cooled down inside by the time I opened up the door.
I'll take some more pictures when I have some time this week and after I wash my car (letting the Xpel Fusion ceramic coat cure before I wash it), but here's a quick pic I took after getting the Xpel PPF, tint, and ceramic coating on my car. I'll also take some more pics of the inside to show how dark it really is, but from the other pic below you can see that the sunroof is pretty dark in comparison to the rest of the windows. From the outside, the tint is dark enough to where you can't see stuff on the seats, but light enough to easily see people inside the car when you're 10ft away from it.