If the coats shoulder front is doing these things to you then you have forward pitched shoulders.
run your hands along your shoulder. You can feel a slight curve to the front, this is normal.
But you may have a pronounced curve. Thats what tailors call foreward pitched shoulders.
On m2m, and on custom/bespoke garments just call the tailors attention to this and all is well.
But on rtw suits, alterations are needed. Its called shifting the shoulders.
Flip up the coat collar. See the different cloth, its the under collar. And the cloth of the suit extends under there. All depends on how much cloth is under there. At least 3/4 to 1 inch. So here is how it goes.
The sleeves are removed, also the collar is removed except where it is attached to the lapels.
The shoulders are also opened up. all the linings are opened where needed.
The first diagram shows the neck hole exposed. the larger curve shows where the under collar was sewn.Now the front shoulder seam is shifted outward and sewn in that shifted position
Check the dotted lines. At the neck the cloth that was under hidden under the collar moves out.
And we have a new curved line at the gorge where the collar is reattached.
At the arm hole we now have excess cloth see that dotted line. This excess is cut off and we have a new armhole curve.
Now all that is left to do is to put all the pieces back together.
As long as the sleeves are detached, they can be re hung to suit your arms pitch.
At an extra cost naturally.
If you copy this and show it to your tailor, be sure to tell him this is an alteration. It is not a cutting table job for making a new garment. He will have to do his own pattern work to accomplish the same results.