Scifi,
I agree with Crazy V, Gonzo does know his stuff!
Take two of the same aircraft types. Both are fitted with exactly the same thrust and operated to the same SOP's. Given that they are flying to different destinations with different assumptions in the takeoff perf calculations and a different load, they aren't going to follow the same vertical path... Take two different types and the equation gets worse! Takeoff flight paths cross, it's the way it is!