Why wouldn't you join a bottom agency?

The top agencies are the top for a reason. Just because you want - doesn't mean they need. It doesn't work that way.

www.newmodels.com

It is based on your looks/stats. (5'10 ish, 34-24-34, good facial features = agency standard)

Unless you are famous/very wealthy.  Then you make your own rules.

For those of us who aren't famous/crazy rich, being as close to agency standard as possible is the best way to get an agency.  You may not have to perfectly fit the fashion mold to do commercial modeling, but significant deviation dramatically reduces your odds.  A thin build and height is still needed, even for commercial work. 

If you truly are curious about getting representation, attend open call (if they have one) or submit photos to agencies.

I don't really know any agencies that specialize in those areas. You are kind of in the netherworld at a size 8 though - too big for fashion (0-2-4) and too small for plus (10-12+).

The best thing to do is apply and see what happens. You might want to look at many agencies and see how it goes. Not to adjust your expectations but you mention top agencies and IMG in particular.....do you have any idea how picky IMG is?