Re: First focal plane.
If your question is whether changing your power changes your point of impact, the answer is it shouldn't.
As for other questions about the desirability of FFP scopes, here's my file on that question:
For punching paper, where you'll dial your elevations and perhaps your windage, a second focal plane scope is fine.
If you're going to shoot tactical rifle competitions which involve moving targets under various conditions, and multiple target engagements at various distances with time limitations, so you won't have time to dial elevation changes between targets, a first focal plane scope is a distinct advantage.
You can use a FFP reticle for wind holds, moving target leads, holdovers and holdunders, at <span style="font-weight: bold">any</span> magnification you choose. With a SFP scope, you cannot - the reticle marks are accurate at only one magnification.
The advantages of a FFP reticle are even more pronounced on a two-way rifle range, where the targets are people with weapons, and they are shooting back.