The fact that it is a complicated equation should increase the need for making a simple way to communicate the data to the player.
Unless you mean it is more complicated than we understand (because we don't have access to the relevant code)?
[I'm not sure what you mean by advisor prompt; I would want this to be information you got even if you had turned the tutorial advisors off.]
I interpreted Thal's post as meaning that an accurate warning isn't feasible.
Why? The mechanic isn't fuzzy; you either get a penalty or you don't. It is binary. And so it should be communicated to the player in that way.
If you're saying that you don't think the penalty should be simple then I would disagree as well, that would seem like unnecessary complexity. I don't see any reason for Catherine to care more or less about you taking her land than Washington would.
I said the mechanic isn't fuzzy, but that my view of the underlying concept is. In my opinion Catherine may not just care more than Washington - she may care longer. This could be the case due to any number of circumstances (which Civ happily provides). To be clear, I know that the game isn't likely to do this any time soon.
Why would you prefer mechanics to be fuzzy? Civ works best in areas where the mechanics are really clear. If you work this tile, you get exactly X food/hammers/gold. Technology Y costs exactly Z beakers to research. A factory will increase city production by A. Imagine how frustrating the game would be if these mechanics were fuzzy.
It works less well in areas where we don't know what is going on (like in combat calculations, where we don't actually get to observe the probability of various outcomes).
As per above, I would want a fuzzy mechanic in service of an ideally fuzzy concept such as "attitude." I would not want a fuzzy mechanic for production or research, unless the game were to become so complex as to allow for weather, etc. The latter would also be difficult to balance, whereas "attitude" is already accepted as unbalanced - Alexander responds differently than Harun.
I'm also unclear as to why you think that "I won't attack you right now" is necessarily informal, or should be. It seems terrible design to me for a player to not know if an action is viewed as a breach or not.
I view it as informal because it's not a treaty. Again, I would like to know how long these understandings last, so I have a rough sense of when it expires without micro-management. My subjective preference is to not get a warning about it, but would have no problem if the game did warn us.