Sending commands to mpv

I'm trying to send back arrow to mpv when I press F7 and forward arrow to mpv when I press F9, but I'm having trouble sending keystrokes to applications.

I'm using the "send shortcut to specific application" setup, and it only works if I have "bring app to front when sending" AND the application is actually being used (in the front?).

I can't send a specific command to an application without it being the focused application AND having that checked... any ideas on what I could do?