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.
Are you just going to get a rapier around with you everywhere you go and fight with one arm behind your back? The only skills you're traveling are the fitness you've gained from training, which is less than that if a runner.
I'm not a particularly tall guy, around 6'. I wrestled during my youth and completed against guys that were 5' tall and others that were 6'5"+. Both heights had advantages and flaws, but universally, if they were well trained, their height was irrelevant to how skilled they were. Agility is something that can be learned and isn't a unique trait that only you possess and that tall guys don't.
I can say with absolute certainty that if a guy, tall or short, wanted to attack you, they could close the gap in the amount of time it would take you to get out, open, and ready yourself with a knife. Maybe if they were 100 yards away and yelled that they were going to attack you you'd have a chance.
Also, what does being sneaky mean in a fight? If you're actively in a fight, you aren't sneaking around. I think one mistake your making is that there are rules in a fight. There aren't. Let's say you have a knife with a 3" blade out and ready to go. If I bullrush you and at the last moment jump up and aim a double leg drop kick at your chest, your just hoping to make contact because the fight is over if you don't end me right there.