Thank you, Sheilajeanne,
Yes, there is a curve at the top of the shoulder. When I make these, I take two measurements: 1) the total length of the player’s current strap (from the centre of the back pin hole to the centre of the front pin hole) 2) from the mid point at the top of the shoulder to the front pin hole when the player is wearing his/her guitar in a comfortable position. I have a few templates for the main portion of the body and cut the front and rear “tails” to the proper length.
It is a lot of work but the contour and the “cut to measure” narrow tails at the front and back reduce resistance and make for a more comfortable strap.
The photo below gives you an idea of how the contour looks