I asked the lovely folk of the Historical Sewing Monthly for some advice. I also canvassed the madly creative bunch at Sewing for Steampunk and Cosplay. Sometimes you just can’t see the wood for the trees can you?
The blindingly brilliant advice I received, which honestly hadn’t occurred to me, was to take the cover off, turn it inside out, reattach, and take up the excess at the seams. Doh! Of course! Damn fool Fairy!
I also let my mathematical brain have some space- with all that tension at the bottom edge, and all those curves on the 16 panels, too much hem allowance would be adding in too much tension AND too much to the circumference AND too much to the length of all the panels. I sat and basted the hem, and then trimmed away as much excess as I could manage, fretting the whole time in case I did my usual trick of chopping a V into the main fabric. PHEW! It survived.
The whole thing fitted much better, the tension brought the ends of the ribs in a bit and gave me the desired slightly domed shape [which the original DIDN’T have, probably because the silk was too perished to provide tension.]
A few pins around the top, and it’s looking good. I’m not going to try to be a perfectionist, as the lace overlay will be gathered in any case. The main thing is to get the inside looking tidy.
Not bad eh?