I have aphantasia and wasn't seeing how it'd have a particular effect on FPS games, at least the ones I've played.

Crosshair placement for things like leading shots? Or more for building a mental map of where the enemy is likely to poke their head up? I would think these things involve spatial imagery/memory. I do remember putting a tiny piece of post-it note on my monitor to act as a red dot sight in Killing Floor, but my guess is that'd help anyone headshot zombies better, not just us aphantasics.