Socializing Is it always game over to approach from behind?

[Maverick2.0]

I found a few niche times where it seemed unavoidable and chose not too approach, like a girl and her friend sitting at a full bar or when a girl is using a machine at the gym that's pushed up against a wall and facing the mirror. Feel like I'm missing more opportunities than I should.

 

[OldGuy]

1. Go up to the bar between them and ask the bartender for a drink. Even if she complains about cutting between them, say "Sorry, did not realize you were talking" and then notice here and start talking to her.
2. Catch her eye in the mirror. From there it is just like an approach from the front.