You will always need to use your mil dot adjustments if shoot above or below your scopes zero.
With an FFP escape, your reticle will change in size as you increase or decrease zoom on your scope
so your mil dot calculations will remain constant regardless of the chosen zoom you use.
With an SFP scope, the reticle remains the same size regardless of the magnification your using.
The mil dot calculation will be set to a specific magnification.

ATB,

JP