While this answer (How to make auto-completion case sensitive? - ac-ignore-case) works in some cases.
Using evil mode on its own.
Adding (setq ac-ignore-case nil) to ~/.emacs doesn't make completion case sensitive. (Pressing Ctrl-N in evil mode).
From looking into it this calls evil-complete-next.
Checked the source but didn't see any options to adjust.
Can this be made to be case sensitive?