No problem. I don't get into much discussions lately, and RoS is still my favourite RPG, so I do not consider it a wasted time.
Actually, the opponent can't attack. This was explained in Companion: when using Stop Short or Toss, the opponent does not declare his maneuver, therefore he can not launch his own attack. In Toss, he may choose to dodge or not, but nothing else. In Stop Short he does not get any choice.
Only when the situation is Red/Red, Stop Short and Toss work exactly as you stated (he launched an attack already).
To be honest, never got stabbed so no real experience to extrapolate from. But in a way you are correct: when attacking belly area, you can hit the sides, which has only single level (disregarding the amount of actual damage you roll): you pierced a flank and there is only little shock and almost no blood loss.
So if the opponent is cutting, he will hit you.
This is valid for most level 1-2 wounds: if you go red-red and you do not hit hard enough, you may get hit easily - and a smart opponent will definitely use the option to increase cut damage by 1 for 1 die (if you hit, it's like an automatic success... and if you do not, it's quite possible the single die would not make a difference).
It's actually possible to make several "troperific" villains. One of my players was actually very combat savvy (he knew the rules quite well and could work the system) and played a ranger/tracker whose weapon of choice was a hatchet and knife, and another was playing an overconfident fencer.
They met a leader of enemy army when they infiltrated his outpost - and decided "to hell with stealth, let's kill this guy". He was actually quite adept fencer (CP around 17) and was considered a "boss" encounter, meaning he got his own SAs.
You know the trope when the enemy is actually overjoyed they finally get to fight someone and then are a bit disappointed? I pulled it off perfectly. He was able to counter anything they threw at him (some luck involved, but mainly tactics, longer weapon, good DTN and they were already fatigued) and after three hectic rounds where I split dice between their attacks and went mostly defensive I pulled off a full evasion, went into aggressive stance and stated "Well. Not bad. My turn now."
They went on full evasion and fled.
It will be a bit tricky to estimate the threat level, but I'll just make assumptions and you can correct me if I'm wrong.
I actually do not know the setting.
One thing: a fight is not inevitable - in this case Intimidation checks are good thing as you can either make the opponent step aside, or make him defensive (if you roll high enough) and even make him lose some dice if you get too good a roll.
But let's assume the captain is determined not to step back and goes for her sword.
Correction: these are not Passions, but Drives. The latter could be interpreted as Oath.
If you are directly opposing your SA, you can lose points you have in it (e.g. if you swore an oath to become a great solder and run away from first battle even though your side is winning), but you do not take penalties from SA. There is one exception: anti-destiny.
For the captain, I'd go with schiavona, arming sword or backsword - longswords are not single-handed by default (your choice, if you actually wish to go against a longsword, no problem there - but she'll go two-handed, as it makes sense without a shield).
I have built her as relatively experienced, on par with starting character in some ways. She'll get an SA (oath: to protect the book at all costs).
Advantages are on your side. Question: do soldiers wear any armor in this setting?
Very well, to arms then.
...
Captain Valzer seems unfazed by your threats, but she draws her blade and steps back into guard only moment after you do, ready to receive you.
OOC: In this case, we are on relatively even meadow, in the middle of forest. There is a shallow brook just few steps to the side, and trees are just few yards behind each of combatants.
Choose stance (Neutral for me; I choose first as your REF is higher)
Throw initiative.