The upswept will work on some shapes, usually a slightly curved back and/or croup high. Curved trees imo are for high withers, usually having big deep rear gussets to balance them, curved panels for shapely wide backs with low or no withers...just to complete the picture from my point of view
Trees and panels vary so much, then there's how much actual space for the rider's bum (flatter seats have more room than deeper for example) and then there's the flap design and whether it pushes you back. Then we have to look at how big your bum is, how long your femur is, what activities you need to do and how short you will need your stirrups, and the best way to accommodate all this.
Also the overall footprint has some effect, so a GP or jump may need to be a smaller seat size than a dressage, even if they're on the same tree (the range I fit uses the same basic tree shapes across most of the range). So many things to be considered. A very flat short panelled 16.5 GP may have a ton more rider room than a deep seated 17.5 dressage or minimal showing saddle.
Then there are brands that run super small, Fyldes run 1/2"-1" smaller than pretty much anything else, in how they fit horse AND rider. So often the source of "but my 14.2" takes an 18" saddle!"