hmmm it really sounds like were just going to have to fiddle with the pattern till it looks right and fits right. I may post a pic so you can see where it sits at the neck and how to make that 'v' in the front lower but keep it where it sits around my neck.
Yeah post a pic... its worth a thousand words...
I do know what you mean though, about the collar standing up when its supposed to curve close to your neck. It's not the trim cut, it's the cut of the tunic pattern that affects that... I'm pretty sure.
Ani's got good advice too... I've done that as well. That's how I made my undertunic pattern. I found a ladies pajama top at a thrift shop that had the shape and fit I wanted, so I cut it apart and made a pattern.