I know I’ve read about this before here but just came across a video with a player slanting his koma …
According to comment below the video, “Its Shibutani Kazuo Sensei style .it helps the ichi no itto( thick bass) sounding more bass and also helps to find the correct positions fast whole looking the fingerboard in an angle …”
I’m not sure I get the helps finding positions fast concept with a slanted koma though.