Thank you for the post and to answer your question it was the cover garment. Having a wide berth of cover garments is key to any solid concealment strategy.

As far as garments go, I tend to find T-shirts or polos are easier to clear than button-down shirts. With button-down shirts, I find I have to leave the bottom button or two open otherwise I have a hard time getting the shirt to clear on the draw stroke. Specifically, I find button-down shirts tend not to be as “stretchy” of material when pulling them up.

The picture of the student appears to be that he is wearing a button-down shirt.