This is kind of confusing, youre saying that Shinichi and Ai are basically fire and ice, and Ran and Shinichi are fire and fire. But there's some questionable points in this argument.
First of all, if anything, Haibara is more like Shinichi than Ran. Haibara and Shinichi both like the same sport (soccer) they're smart, have interesting lives, both grounded each other, both understand each other, both attracts opposite genders, both know Sherlock Holmes (Ran does too, but she gets tired of Shinichis constant blabbering of him) and others things. Whilst Ran and Shinichi, have the same ethical thoughts, attracts opposite genders, but that's about it, there may be others that i haven't covered but it still not as much as haibaras.
I admit that Shinran is 99.99% the end result, but I'm just stating the flaws of your statement. Sometimes, I even find opposite attractions my sweet, but ok.