I'm 6'2" and I checked the seat room before settling on the drill location. I can't put my seat in the position your describing. You could drill back farther and have the back of the screen sit higher on the seat belts. If you look at my picture, I would have had to go back quite a bit to miss...
Without the holder the belt vibrates annoyingly (feel it across my chest) with the top down, above 30ish MPH. While in the holder, retraction is quite poor but the vibration stops.
Just got a 2019 GT, and in sport mode on the 350 mile drive (fly and buy) home this "lag" was very noticeable. I'd hold rpm steady at say 3K, then apply an extra ~30% throttle. I tried gears 4-8 with this process and all exhibit it. Feels like lean CV carbs on a motorcycle.