I just confirmed that mounting the shield further back IS more secure.
I removed my barrel and placed my modified shield on it. It fit loosely in the foreword position I had it at. I then slid it back to where the barrel swells and it held much better.
So if you plan on doing this mod, be aware that mounting the further back, the better. Due to my setup with the light and SRO, that wasn’t possible, so I will live with the ranger band…