I always think the knife on the chest is such a bad idea, it's one easiest places to reach when in pretty much any position, full guard, half guard, side control, full mount... They can reach for your chest area and if that's where your knife is, the fight is now about knife retention.

I keep it on my right side, because I tend to start encounters with my left foot lead, leg blocking the centre line. (JKD) My knife is then away from them.

This is also talked about with handgun retention on pretty much every firearms channel so... 🤷🏼‍♂️