I notice that even with weakpoints scanning enabled for Vanga it will still try to lock onto pieces of the enemy tank that are behind an obstruction/ground/building etc.
I tried using it to fight a chinese heavy armor peaking his turret over the hill shooting at me but Vanga kept locking onto his hull that was easily hidden, but his commander hatches were visible to shoot at.
So far, Vanga hasn't been useful for anything other than shooting at fast moving scouts that are suicide rushing to our artillery. Vanga keeps locking into pieces of the enemy tank that won't do damage or will always bounce (tracks, or side-skirts that absorb all the dmg).
I did find vanga useful for randomly taking pot-shots at enemy at long range without much trouble switching between targets, but i rarely got a hit :P.
Cheers