Odd question, but what size bottle nipple do you bottle feeding momma's use? We use Avent natural flow bottles and just tried to switch up to size 4 (6m+) and she HATES them! There's no issue with the flow it seems to be the nipple feel. We have tried for a few days now but she just pushes them out of her mouth and doesn't even come close to finishing her bottles. I think it's because this size is thicker than the others and less flexible. We admit defeat and dropped back to size 3. Tell me I'm not the only one?