With a mounted plow, the 3-point top link SHOULD be straight in line (front to rear) with the centerline of the tractor. There is SOME leeway with that, but "in a perfect world", it should be straight.
In that same "perfect world", you set the tractor to match the plow, and NOT the other way around. Any plow has what is called the "line of draft". That is essentially the center of the work load.... That lime of draft should be centered behind the tractor, THEN, the furrow side rear wheel of the tractor should be set just to the outside of the front bottom. On a typical 2-bottom plow, that is 22" to 24" from center line to inside of rear tire sidewall.
That width changes (increases) with a 3-bottom plow (or larger)
With the majority of newer tractors having all sorts of different tire combinations, (ie R4,s turfs, ect) and the lack of adjustability of track width, SOME deviation from "the rules" may be needed to get a plow to track behind any given tractor.
As far as the offset drawbar..... The offset is there to level the plow when furrow side wheels are in the furrow. Rotating that drawbar is NOT to be used to level the plow from side to side..... That's a job for the leveling cranks on the 3-point hitch. Rotating the offset drawbar will skew the rear of the plow left or right depending on which direction the drawbar is rotated. That will put more (or less) pressure against the landslides, which will in turn make the plow want to follow left of center or right of center. (and you DO NOT use stabilizer bars/links on the 3-point hitch to hold the plow where you want it.) Skew the rear towards the furrow and the plowtends to track to the LAND side, as pressure against the landslides decreased.. Skew the rear of the plow towards the land side, and the plow will track towards the furrow side, as pressure against the landslides is increased.
If you have more than enough tractor (weight and hp) for the particular plow you're using, it's possible for a tractor to "manhandle" the plow when it isn't in proper adjustment. If you're operating anywhere near peak draft load, a plow would need to be "by the book" or else it would pull like the proverbial boat anchor.
With a well designed plow, attached to the tractor correctly, and everything in proper adjustment, and the plow glides through the ground ALMOST effortlessly. Deviate from "perfect" very far and you suddenly have a fight on your hands.
Think of a plow in the ground much the same as a rudder on a ship. If it is locked into position, the ship won't turn. A plow needs to be able to move side to side in order to allow some degree of control with the tractors steering. With a plow setting dead level when in the ground, you minimize the plows tendency to raise up out of the ground. Minimal wear on the shares is the key to "suck". (The plows natural tendency to pull itself in the ground) Too much nose down attitude, and the plow wants to keep pulling down, creating excess load on the tractor. Too short on the top link and the plow dives into the ground. Too long, and it tends to want to raise up. (or never go in the ground to adaquate depth) "Just right" with the top link and the plow pulls easily and has but a little compression on the top link, nor will it have excessive tension on the top link. And as mentioned, side to side directional control is acheived with rotation of the offset drawbar. It's just like sticking your hand out the window of a fast moving car....hold the hand flat and everything is effortless, but curve the hand and it wants to go up or down....You want the plow to pull as lightly and effortlessly as possible.
But...Since we aren't in a "perfect world", and tractors today are NOT designed with moldboard plows in mind as a primary duty, you have to make compromises with any adjustments.
Thanks for the set up info....