Do not fall into the trap of self-fulfilling prophecy, where you change tire pressure and see an improvement in lap times--then conclude that you have discovered a profound tire pressure to best grip relationship. If you are convinced that a tire pressure change resulted in an improvement--go back and test the previous setting AND be sure you drive the car just as hard. A confident driver is a fast driver, and often we grab hold of settings where we have become confident, and simply drive the car harder with those settings and higher confidence.
As mentioned earlier, this has been a "bone of contention" for some time and the consensus is that it has improved. (While we all know that drivers at Indy tend to pay attention to sun and clouds during qualifying--some think iRacing has overdone it a bit.) Related to this is science that teaches us that at the limit, a portion of the tire contact patch is in the "scary-exceeding the limit" while the adjacent portion is not--so if iRacing's Tire Model places a high degree of grip variability in relation to temperature, this may explain why some feel the "scary" zone is more scary than racing tires in real life.