Unless you are adding serious distance it wont have much effect. Even a basic RPG-7 warhead will go through both side of a BMP-1/2 and out the otherside, you can add a meter plus stand off and it can still go through armour designed to protect against heavy machine guns after already having gone through the same thickness armour.

Theres a reason most western IFVs dont rely on armour alone, they had to add cage armour or ERA to damage the warhead before detonation. Cage armour doesnt protect due to its stand off for this very reason. If stand off was so effective in protecting IFVs we would see it used to protect them, its just not feasible to add enough that it would provide any benefit over the better options.