I know something isn't right because I see my buddies going through those holes and then I go through and they say it looks like your boat was completely vertical. Thanks again
You can't read too much into that. In a boat with as much distributed volume as the new Mamba, your seat position isn't really going to have so much effect that your boat will tail squirt etc. In a short playboat this would be an issue, but I doubt it would be so in a Mamba.
You stated that you are new to kayaking, and so I would start by looking at your posture. I would make a fair wager that as you go over the drops into a hole that you are allowing yourself to lean back, thus causing instability, and in some cases causing your boat to go vertical.
Further more it may be because your stroke timing isn't there you don't have enough speed/momentum to punch the hole, which again can cause you go vertical depending on the power of the hole.
How heavy are your friends? If they are a lot bigger than you it may explain some why they can get away with punching through stuff more.
I would recommend leaving the seat position alone, keep it in the middle, especially as you are at the low end of the weight range for that boat. Instead focus on your posture, and the timing and quality of your strokes. It is all too easy to blame a boat setting when it is most often actual technique that is at fault.
This isn't meant as a criticism, just something to possibly refocus on. Any video of you doing a run?