After many experimental haube (coif) mock-ups, talking it through with Lady Antoinette, and feedback from the GermanRenCostume Yahoo Group (especially from Katherine), I have a preliminary pattern for the goldhaube:
The haube band would be sewn to the straight side of the haube itself, which would start at the top of the head (a bit back from the hairline) and tie at the bottom back of the head. The rounded part of the haube would be gathered (or smocked?).
The under band would go across the top of the head at the hairline and tie at the bottom back of the head. It goes on the head first, then the haube goes over it, covering the top and back of the head.
And the reason for the grain line is that I found that cutting the haube on the bias allowed the material to stretch over the braids on the sides of the heads in a more fluid manner. It would also explain why I see pearls applied at 45° angles to the line of the haube — they would be along the warp and weft lines of the fabric then.
I’m continuing to seek feedback before I proceed!