I'm trying to figure out the math of vassalage for the 100 Years Scenario.

Leaderboard tops have whittled it down to 15 turns!

From the HUMANKIND wiki:
War Score = WS_start + WS_end + C₁ + C₂ + ... + C_n

Or in the scenario:

War Score  = WSstart + W_Send + C_London + C_Bordeaux + ...

(*WS = War Support).

C_x = 30.

I've been trying to DoW when I have 100 War Support, to maximize my War Score to be able to vassal England. 

In my last playthrough it required 220. (But if you DoW earlier it can be less. E.g: 190).

In my first playthrough I managed to vassal England with just London, but on subsequent attempts I took out both Bordeaux and London.

(In fact, Bordeaux is the easier target). But on both occasions I took Bordeaux, I had to also take London.

But I am wondering about the Leaderboard tops who have managed this in under 20 turns.
The math suggests they rely more on taking both English cities ASAP and maybe DoW before 100 War Support:

Taking both London and Bordeaux gets you 60 War Score.
The rest, 160 War Score has to be garnered from War Support.

So that means start the war with a minimum of 60 War Support? Surprise War?

Discuss.