Mark rippetoe doesn't say your upper arms should be perpendicular to the ground
You can't rest the bar on the shoulders if you do that. Maybe you meant forearms should be vertical? But that's still not correct
Well i thought forearms = upper arms.
And i checked out the video once again, he did say forearms vertical/perpendicular to the ground. You can rest the bar on your shoulders that way, try a bit wider grip width and you will be able to rest the bar on the shoulders