While searching for some other conversation I've found an old comment of mine in a Facebook group, a comment documenting the relative measurements of my Regency dress compared to my figure. I thought it was worth reproducing as a (more detailed) blog post for future reference for anyone who wishes to achieve this sort of early 1800s columnal style on a more "feminine" figure with bigger hips. Since mine was achieved through trial and error but I'm really happy with how it turned out in the end.
So here goes one person's experience:
I'm wide-hipped, approximately DD-cupped, but pretty slim.
My underbust measurement is c. 75 cm (29,5 inches), my hips are c. 102 cm (40 inches); 1,36 : 1 hips-to-underbust ratio. The vertical distance between the two is c. 40-42 cm (c. 16 inches). My bust span is c. 20 cm (c. 7,5-8 inches).
The dress has rectangular front and back panels, with gathers in the back and trapezoidal gores at the sides (more like side front I guess). The front panel is 24 cm (c. 9,5 inches) wide (= with 2 cm on each side in addition to my bust span). The gores are 18 cm on top and 29 cm at the hem (c. 7 & 11,5 inches). The back panel is 115 cm (c. 45 inches) wide, gathered into the waistline.
So it all adds up to 172 cm (c. 68 inches) at the waistline / underbust level, compared to my 75 cm (29,5 inches) measurement; 2,3 : 1 ratio. A lot of that is taken up in the back gathers. It's a drop-front dress, so there's also some overlap between the side gores and the back panel.
The skirt is 112 cm / c. 44 inches long at the front & sides (slightly longer in the back due to the raised waistline there).
The hem is 2,5 m (c. 98 inches & 2,7 yards) - so it's c. 2,5 : 1 compared to my hips measurement, and c. 1,4 : 1 compared to the skirt dimensions at the underbust level.
All this in a very lightweight cotton sateen. There are tight gathers of the two rows of running stitch kind in the back; about 60 cm (c. 23,5 inches) gathered into about 10 cm (4 inches) - I'm not sure how much exactly it was anymore, this was just a very quick measure at the hem, but 60 cm kind of make sense to me as a number I'd have picked. :D I underlined the thin fabric with a strip of cotton plainweave so it's a bit thicker and not quite as much fabric is taken up in the gathers as it would otherwise take in something as lightweight as my sateen (it's a lot anyway - 6:1 ratio!). Then gentler gathers towards the sides.
Now you may not want to reproduce the exact proportions of my pattern pieces - my narrow front panel is a bit weird to be honest - but hopefully putting it down in exact numbers and proportions like this can help you decide how to proportion your dress if you're struggling with that. :-)
You see the trapezoidal skirt patterns more often on later, 1810s & 1820s dresses, but they do sometimes appear in dresses dated to the earlier, more strictly neo-classical era as well. Based on my own experience, they may well have been an invention to accommodate wider-hipped figures similar to mine who wanted the sleek columnal look with full enough skirts for movement and without putting too many gathers at their underbust level.