My BCI never ever burrowed himself in substrate. The only time he did it is when i moved him to his adult enclosure and took his hide away. He kept burrowing until i gave him his hide back. Give him/her a hide and they won,t burrow. This is what i have experienced so far
Oh? Roe has two hides in her tank, a big rock corner hide on her cool side and a small log on the warm. I've had these in there ever since I got her, and she's always burrowed