FTF of a high primer = first firing pin strike seats it (causing a dimple). Second hit should fire it. If not, then chalk it up to a bad primer or weak hammer spring. Depending on frequency of occurrence.
I've got where I run the side of my index finger under each case as I prime it.
and when I run pistol rounds on the dillons I take each bunch and put them bullet down in a MTM case so I can check the primers before dumping them in the storage containers.