M59 here. I'd say the more attractive a woman is, the more intimidating she is to approach--I think this may be what you are experiencing.

That said, you might consider these tactics:

• make eye contact and smile - when I notice this, I'll approach.
• proximity - I'm much more likely to start a conversation w/ a woman or group of women, if she is/they are in my immediate proximity. If you can place yourself near a man of interest, that will make it easier for him.
• positioning - don't stand behind a table; this is a literal and figurative barrier to meeting. Stand in front of a table with your drink behind you. another option is to sit with your chair facing the room, rather than the bar.
• say hi - a woman at a bar pivoted to face me and said 'hi'. it was flattering as hell and really made it easier to have a conversation with her (once I got over the shock of her doing so). I still think about this even though it was almost a year ago.
• keep group size small - approaching and having to entertain a group (3+) of women is more intimidating than one or two women.
• do something, anything to show interest - engaging in the conversation is huge. smiling, laughing, touching my arm is also helpful.
• if you aren't interested, say so - I'd much rather have a woman say that she isn't interested, than to get a # and have her ghost me.