I've come to my conclusion with the problem. Whether it is right or wrong, I guess we will find out on Friday.
Let me explain. The issue is two fold.
1. Blocking the antenna of any cellular will degrade the signal quality. This has been confirmed with multiple other devices.
2. The iPhone formula for calculating reception is actually terrible. If you have seen it, you will understand. You either have 5 bars or none. The jump in dB from 5 to 0 is very small.
Number 2 is the key here. Think of it this way: The dB jump from 5 to zero bars is very very very slight in the current formula. If you are already in a low signal area, you should be displaying low bars. Currently, this is not the case, because the formula is wrong. On top of that, you begin to clamp your phone, blocking the antenna, therefore degrading the signal quality even more than the low quality area you are in.
I have never been able to replicate this issue in a good signal area. Only a terrible one. If someone can stand under a cell reception tower, and replicate this issue (5 bars to completely no service) I'd see the death grip being an issue.
But the fact remains: blocking any RF antenna will degrade signal quality. This is fact. It just becomes amplified/dramatized under apple's terrible formula.