Hello, 

when we use formula of nMV = nMV, that doesnt require the balanced chemical equation, thus it's not 2:2 ratio. 

Let's say if there's 200.mL of 0.1 M HF, then you need 100 mL of 0.1 M Ca(OH)2 solution, right?

Since nMV = nMV, 1 * 0.1 M * 200 mL = 2 * 0.1 M * 100mL. 

However, if you use the balanced chemical equation and use the molar ratio of coefficients as 2:1 for HF to Ca(OH)2, 

then 0.1 M * 200 mL : 0.1 M * 100 mL = moles of HF : moles of Ca(OH)2 = 2 : 1. 

Then choose either way, it will work anyways, but do not mix two methods. 

Either way will give you a same answer!!

Hope it helps!

Kelda