We will be glad to add darts.
Though not traditional, darts are essential for a contoured slim fit.
As the front of the waist part of the body is often more of a concave and the back more of a convex, just adjusting the waist is not always enough. The shape/size of the chest and upper back play an important role too.
How do you specify how much cloth and where exactly to taper for the darts? Or do you have standard darts?
Btw, I sent Theresa two e-mails this week about advice for the fit of my first shirt (order 4404) but haven't heard back yet.