I've had curvature issues with TheSky6 mosaics. It's almost like as if each panel needs 1-2 degrees of rotation to fit.
Rick's right; make a scaffold mosaic first -- that is, take a 30-second exposure of each (I use a 10-20% overlap -- to help account for the curvature issue) and then join them together to see if it's going to work.
Joining mosaics is a time-consuming task.
I can write a detailed reply once I get home tonight on how to do it.
H