When the cart is pushed backward so that the traces are tight (in draught) the shaft tips should be no farther forward than the point of the shoulder. This keeps the lines from getting caught and prevents the horse being poked in the neck.
The shafts should be level, and the tugs (the loops that hold the shafts) should be hanging straight down from the saddle, perpendicular to the ground. The traces should pass between the two belly bands, but not inside the tugs, on the way back to the single tree.
With the cart still pushed back, you can hook up the breeching. The breeching should be just tight enough to put a fist between the breeching and the horse’s rump. So that when you are finished hitching the cart only rolls about 4-5” between the draught of the breast collar and the breeching. This adjustment is what keeps the traces from becoming too loose.
This photo is the best I could find, you can see that the traces are in draught but the breeching is not droopy or loose at all. You can see that the shaft tips are behind the point of the shoulder and the traces are run between the two belly bands.
The shafts are not level, I feel there is some leeway for this rule because your vehicle might have to fit different horses, so a little pointing up I feel is Okay, although never pointing down. If and when I get a new cart for this horse I would make sure the shafts are level though.