We want to do a seat cushion in fabric, not leather, but we want the shape to look like this (catalog cut from a Stickley book):
(https://forum.upholster.com/proxy.php?request=http%3A%2F%2Fi725.photobucket.com%2Falbums%2Fww255%2Fthe3rd%2F2015-01-04_1540_zpsst8dyacx.png&hash=8b1be9a737d49224b113b1d56236d84d) (http://s725.photobucket.com/user/the3rd/media/2015-01-04_1540_zpsst8dyacx.png.html)
Note the front-to-back shape.
We have a how-to-upholster guide from an article by Popular Woodworking that shows the pattern for the fabric and here it is:
(https://forum.upholster.com/proxy.php?request=http%3A%2F%2Fi725.photobucket.com%2Falbums%2Fww255%2Fthe3rd%2F2015-01-23_2219_zpsnjomtzjr.png&hash=081d0711c011014535b8547d28fc48b2) (http://s725.photobucket.com/user/the3rd/media/2015-01-23_2219_zpsnjomtzjr.png.html)
We're concerned that if the fabric is cut with only the small fillet at each top corner (each side panel) that we will not get the shape we see in the Stickley photo.
Should not the pattern for the side be domed with fillets at ends, sort of like this:
(https://forum.upholster.com/proxy.php?request=http%3A%2F%2Fi725.photobucket.com%2Falbums%2Fww255%2Fthe3rd%2F2015-01-23_2221_zps4f4ouuhp.png&hash=f7b9c0a84dbb2f47a7206cb5488ecb68) (http://s725.photobucket.com/user/the3rd/media/2015-01-23_2221_zps4f4ouuhp.png.html)
We are not upholsterers, only woodworkers, and this work will be done by a pro over seat frames made by us. It seems as if the more square the cover, and by that we mean, flat on top with smaller fillets and no dome top shape for the side panels, the more we get a look like this:
(https://forum.upholster.com/proxy.php?request=http%3A%2F%2Fi725.photobucket.com%2Falbums%2Fww255%2Fthe3rd%2F2015-01-04_1538_zpsfn0royrf.png&hash=25c5d1370f671f18951caeadf33147d7) (http://s725.photobucket.com/user/the3rd/media/2015-01-04_1538_zpsfn0royrf.png.html)
Are we right, and if we want the tighter pulled down front and rear look, as seen in the leather-covered Stickley chair, that we should go with the domed-shape side panels?
Inquiring woodworkers want to know.
Welcome to the board. You are quite right, the side panels need to have the shape your looking for.
You can also "shape" the foam cushion core to enhance that crown front to back. My scanner is on the fritz, but here is a narrative of how I'd build up the foam: For sake of arguement let's say want the front and back to finish at 3 1/2 " (4" foam) and the centre 4 1/2 (5" foam). I'd cut a piece of 3 " foam the size of my top/bottom panels and glue a piece of 1" foam the width of the cushion but roughly 4" (you'll want to experiment a bit with dimensions before you actually glue everything together) shy of the front and back. Then glue a piece of 1" foam larger than the cushion on top of that. Trim the top 1" foam to the size of the cushion. I like to use an electric carving knife and use the 3" foam as a blade guide.