I (21f) am 5'5" and skinny. I recently attended a self-defense class, and there I was tought how to use a pocket knife. And as I have some male friends 6'5"+ tall, I thought that that height actually makes their belly particularly vulnerable in case of a fight (compared to a short guy/girl):
- a short person's shoulder height is around the same level as the the tall person's belly making it easier to stab/hit;
- a tall guy's belly is proportionally a larger target.
And in general, if a 6'5"+ guy stands in front of me with his stomach released (even if he has just a bit of a belly) it feels like having an exposed, large and squishy punching/stabbing bag right in front of me, into which, if needed, I can easily harshly and deeply plunge anything straight away.
I also practice historical fencing (rapier) and most of the times I stab tall opponents into the belly - my favorite thrusts are ducking counterattacks when I duck while they attack, go low and impale a tall guy's unprotected belly right onto my rapier.
Well, my self-defense is to plunge my knife up to the hilt into a tall attacker's belly and then if necessary even twist the blade there or move it quickly in his gut so that the attacker gets literally gutted. So, you better don't underestimate me, lol
Maybe look into the legality of lethal force, and the circumstances under which you can use it. A knife isn't any more of an end-all-be-all than a gun is. Nowhere near every situation requires lethal force, which a knife legally is, regardless of the end results.
Of course I know and understand that.
If you want some good reading material on the topic, try "Scaling Force: Dynamic Decision Making Under Threat of Violence" by Rory Miller. It's a lot more complicated than the average self defense class makes it seem, and the instructor doesn't have to answer for your actions. You do.