You notice an excess of fabric and lines running diagonally over the front of the shoulders and down across the bicep when you have your arms by your sides.
The problem comes from the incorrect shoulder width or sleeve width (bicep measurement). Poor alignment of your dress shirt seams with your body will result in having excess lines around the front of the shoulder.
This will happen if the shoulder width is too wide, and the seams of the yoke are hanging off the ends of your shoulders. To solve the problem, you may consider decreasing the shoulder width by ¼” – ½” to bring it up just a bit higher on the shoulders.
You may also decrease the sleeve width by ¼’ – ½” so that it is tighter around the biceps and thus reduce the amount of lines that appear around the shoulders.