Facebook Ads setting help !

Hey guys, just want to ask when we set the audience location in the facebook ads setting, there is a meter down there (refer picture below) showing that how broad/specific of our audience selection...

My problem is when i am going to promote a viral post in my facebook page, should i set it to a very specific location until the meter point to "specific" level or just "fairly broad" will be fine?

Should i just set it between the middle (the green line) then will be fine? Because, whenever i set it like "California, USA", the meter will only in the green line in the meter.. but the potential reach people will be big amount.. around few million people...

However, whenever i try to set a very specific location until the meter point to the red color line in the meter, the potential reach people amount become quite less...

So, i am confuse with how should do this... how you guys set your audience target? Thank you.

anyone can help me?

I've heard answers both ways. What you need to consider is that the more engagement your ad receives, the cheaper that engagement will be. Highly engaged ads receive lower CPCs. So, if you believe your ad will have more engagement per view with a more targeted audience, then that is probably the right decision to make.