Square shaped sweater fit problem

Hello, all! I’ve knit two sweaters now which are basically squares with set in sleeves. The back neck is not shaped, but goes straight across. I’ve noticed that they both tend to slide back over the shoulder when worn, so that the shoulder seams do not lie on the top of the shoulder, but behind it, creating a goofy looking, kinda nerdy fit. with the front riding up! Would this be because the back neck is not shaped? Your input gratefully acknowledged ‘:notworthy:’,

Unless you’ve got square shoulders, that’s probably why. You could try putting in a few short rows in the center back to shape it a little. I’ve also heard that many pattern designers make the back slightly longer than the front which will help too.