After playing with your PDF files in Photoshop, I found if I enlarge them to 112.7%, my dome bottom fits your template front and back, and side to side. The only real difference I see is in the back. My rear "corners" have a tighter radius than yours, so my dome sits inside your template there. But it's darn close.
This is my untrimmed dome.
I'm going with 240mm width and 254mm depth.
The dome cut in quarters (with a little application of heat here and there) fits onto the overhead template for the dome base perfectly.
I've been printing templates all weekend and tweaking them. I just can't get them to mate properly with my dome bottom. The flair just isn;t working out for me. I think the problem may be that I am trying to do the back as one half. Then I was going to do the front.
I'm going to regroup, and try a template that wraps around from the front, with a seam in back. I think one piece will be more fogiving when I try to make the front and rear planes striaght, and flair the sides.
I know what you mean when you talk about wrapping the back as one piece. Very hard. I will make my seam at the center rear of the helm.
I plan on attaching a few pieces of small plastic from the inside of the dome to glue the sides to so I don't have to worry about a perfect mate to the base of the dome.
This is trimmed now at what looks to be proper height......side and front profile shots. Looks about right.