Because this diwan is for one person, we ask a question most furniture never asks: how tall are you?
A chaise has a specific critical measurement - the point along its length where the seat ends. On a well-made one, that point falls just past the back of the knee, so the thigh is fully supported and the lower leg hangs comfortably or rests on the rounded end. Get it wrong in one direction and the edge presses into the back of the knee; get it wrong in the other and the calf is unsupported and the leg gets heavy.
Standard chaises are cut to an average and everybody adjusts to them. Ours are not. Seat length is set from your own height, and seat depth from your build, so the shape arrives already fitted.
The back height is set the same way: high enough to take the shoulders when reclining, but not so high that it looms over the piece.
None of that shows in a photograph. It shows the first time you lie on it and do not have to shift about to find a position.