I think it's just the angle. My support-hand thumb is below the cylinder and JUST behind the B/C gap...I think that's what you're seeing. I've got huge hands, and this round gun with its smaller grip has taken some getting used to compared to the Glocks that I've been shooting for a couple years now.
I will be experimenting with different grips and grip materials as time goes on, but for now I'm just trying to get the basics down pat so I'll actually know what I need before buying.