I agree that 10 might be too small a set. I was thinking 20 but 30 might work too.
The smaller the set, the more you avoid streaks of consecutive misses. But also, the smaller the set, the bigger the difference between actual % and shown %. So I guess you have to nail the perfect trade-off. Yes, 10 is too small, definitely so now that we know what to look for. (hint: 20 would certainly work, if we didn't know about this trick)
But do you also expect to miss 3-4 times in a row with a 70% THC while taking damage every time the enemies attack? The question isn't about statistic or probabilities but combat design.
Yes, I normally expect that this will happen at some point. The better my %, the less probable that it is going to happen. On the other hand, I won't necessarily notice it if it doesn't happen, as evident by my AoD experience. So I understand what you are trying to achieve.
Depends on what THC is. If we take it as your average from 10 or 20 attacks, it's deadly accurate. To have 70% THC, you MUST miss 30%, otherwise your effective THC is 100%. Consecutive misses are a separate issue here. The most important one is representing your THC is accurately. If there's no practical difference between 50 and 70% because "the only truly correct answer is infinite", then raising combat skills from let's say 3 to 4 becomes kinda meaningless, UNLESS it increases your batting average in the course of one fight not the entire game.
Well, you almost got it in your last sentence. Having a small/moderate increase in THC necessarily means that the effect is bound to be "visible" over the course of the entire game, and probably not in the next fight. That's how probabilities work (when they are non-conditional, ie when the result does not depend on previous results -and probabilities are supposed to be non conditional unless otherwise specified). So the goal of the player is to get his THC moving in the right direction, that's all he can do with small changes.
I understand that you don't like this in the context of combat design. OK, maybe I am not a huge fan of it either, which is why I also play deterministic games like chess, but it is what it is. And gamblers (which I am not, and apparently you are not either) love it.
I have never studied this problem deeply in the context of RNG combat design, but two solutions I have happened to come across are the following (in case you are interested):
1) the Baldur's Gate 2 solution. The combat is RNG but also puzzle-like. So the true solution to an encounter is having Plan A, if that fails then Plan B, if that fails Plan C etc. The wealth of options makes this possible, and it is also a lot of fun and very satisfactory (for a nerd like me) to study the system in order to come up with my plan... D or whatever. You do need a very rich system to pull this off.
2) the Legend of the Void 2 solution (flash turn-based game). The RNG is quite random in the beginning, but then you grow in levels and carefully design your builds, and by the end of the game the enemy cannot hit a well-designed party almost at all (by that point the enemy can only hit one of the tanks, but tanks can take a lot of punishment and they are not really in danger if the player knows what he is doing). The satisfaction here is that you have mastered the system, you 've built great defense, and then you enjoy the results. You still need to have your eyes open, because some enemies come up with weird offensive tricks that you need to reply to effectively.
PS. The reason why conditional probabilities are not an official thing, is that they are very hard to calculate for the layman. They are often hard to calculate for trained people too, mind you.