Couple of considerations:
- Make sure you're wearing the right size. I was between a medium and a large, and had to go up in size due to my shoulders being so broad. This made it so I could not get completely flat - so if this is the case for you, you may need to look at other brands that are sized differently. If you switch to GC2B, read as many threads as you can on the sizing. I never owned one, but from what I have read, it's very hit or miss.
- Make sure you're wearing the right style for your body type. I do not recommend the tri-top for bigger guys. It hurts and it looks awkward.
- Consider what you're layering with. I would wear binder > tanktop > t-shirt > maybe another layer, to get completely flat. If you can find a tighter sports bra, consider doubling up and wearing that and the binder. It should help you be more in control of where things end up once the binder is on.
- Consider positioning. The first time I started binding, I just pulled it on like a shirt and went about my business. You should be moving your chest so that it's pushed to a flatter position. For me, the "up and out" towards the armpit region worked best.
