I have made the D9P, (both versions}, a pinwheel quilt made with HST's, a rail fence quilt, a rag quilt made with Courthouse Steps blocks, & a chenille quilt--in making these I learned the following:
If you use a 1/4" seam decrease the stitch length to 1.5-1.75 (my rail fence quilt shredded at the seams because the stitch length was too long to hold the 1/4" seam)
If you don't want to go the full 1/2" seam, a 3/8" seam works well.
Patterns with 6 or 8 points to the center are do-able, but must be pressed correctly to reduce bulkiness. This type of pattern is best done with 3/8" seam allowance.
I don't know if what I have learned is the totally accepted correct way, but I have had only the one quilt shred out at the seams. Love the flannel quilts. Oh, I also use Hobbs 80/20 or Warm & Natural batting.
As others have said, starching a bit really helps, starch from the back side of the flannel and be careful not to distort the damp fabric when pressing.