I can't change the building displays that say 'must be below whatever amount' (well... I can but I don't think I should... that's just the ability of the building itself and that ability is conditionally overridden by any total minimum defense that ends up higher than the amount specified by that building - the minimum becomes how far down you have to get the city since you can't get it any further reduced.)
BUT the only way I think you can see this information is to be looking in the city right? So rather than reviewing the city's buildings to see if they have such a minimum attackable limit, rely, instead, on the Defense hover popup that you can get by hovering over the Rook symbol in the upper rightish portion of the city screen. THERE it should break things down correctly.
Now, if there's a portion of the combat help popup display I'm unaware of I can see why this is confusing. Otherwise, where are you guys looking to rely on your information on when you can attack and when you can't that makes this so confusing? It sounds like I've overlooked a display somewhere. (Or didn't update the display quite correctly where I figured players were already looking for this information in the first place. There COULD be a bug there but I recall it testing out fine.)