Regarding your first tip, I’m not sure where you’re flying, but I fly around the US for work, and they absolutely will send you to the back of the line if you try to board in the wrong spot. Happened to me once recently by accident, got two flights and their boarding groups mixed up. They weren’t rude about it or anything, but they were not going to let me on before my group.
So, first, you can’t be much more confident than an honest mistake. I didn’t even know I was in the wrong group.
Second, they weren’t reading my phone. You turn your phone face down to scan the QR code. They literally can’t read it like that. The system tells them where you are supposed to be, including boarding group. If they’re not trying to put you where you’re supposed to be, they’re probably tired of dealing with people like you.
Lastly, people fucking up the system by cutting in line are a part of why it takes so long to board. If you want to board earlier, man up and pay for a premium ticket.