Something I'm interested in is a list of manufacturers that have their reticle system calibrated for use/ranging on max power... Trijicon is the only one I know of, but I have not researched it yet. Has someone already compiled a list? No point doing twice the work.
Back on topic- I am trying to learn this also. I like the fact that the reticle stays in relation to the target's size at any given power in a FFP. This means an MOA is an MOA or a Mil is a Mil at any power and thus can be held for wind on any power, for your cartridge, which means practice.
This can be figured out for a SFP scope also, but would take heaps of drop charts and shooting in all given conditions at all different powers... right?