Ebony Dragon
Explorer
It would be easier if you used clearer, simpler wording.
Any time you use the phrase, "fictional positioning" (and you used it three times in one paragraph), you are losing a chunk of your audience. It's unhelpful jargon.
I'm starting to feel like the majority of this thread has just been people fictionally positioning themselves.
Rules should be clear and include as much as possible. Of course, as a DM you have the power to analyze specific situations in detail that the rules are probably only covering generally, so you always have the ability to rule zero. There should be a good reason for it though, as characters are created and played assuming certain rules work in certain ways.
Whenever you rule zero something like "diplomacy doesn't work on this guard, I don't care how high you rolled. Sorry" you are in a small way invalidating this players character concept and his belief in how the game system is supposed to function. Do it too much and you have the potential to lose that players trust.