Firstly I have to point out I have alot, and I mean alot, of experience with the Diplomacy in this game. I have to point this out or my reply could be seen as a waffler or a discontent player just ranting. I am neither (well a bit discontented with a specific bug atm but that dont count).
I find the Diplomacy in this game to be very uninformative for the player, it hides alot to do with the --- and +++ it uses in the UI, some of these modifiers can range alot more than a --- (-3?) or +++ (+3?). I had hoped that the new expansion would have fixed this uninformative nonsense tbh. And yeah its nonsense to me when a + can mean +1 or +10 and a - can mean -1 or -10.
I do understand your frustration or confusion in regards to the 7 ships changing things dramaticly like it did for you, but, it can, that is all down to how "powerfull" the AI think your Military is. This can change from day to day with the AI, it has one of the largest variations when it comes to the modifiers that effect it. (Ships, Ideology and Personalities)
I totaly agree with the DoW's when said Civ is completely out of range, this is down to the fact the Out of Range modifier seems to cap at +10 but the Rip for Conquest has no cap and can end up -30 or more depending on how weak they think you are. You could fix this with a simple (double the value for it) xml edit btw (DiplomaticModifiers.xml).