It would be useful for those of us who use vertically-oriented monitors to have top/bottom thirds & two thirds options. There are existing left/right equivalents, but not top/bottom/vertical middle.
this can be done using the "custom move & resize" action 
I can post the necessary configuration later (currently not at home) in case you need help.
I finally set this up and got the top 2/3 configuration to work, but this bottom 1/3 configuration seems to just fill the top 2/3...
FWIW, I came looking for this exact feature, for exactly the stated reason: I use a 90deg rotated monitor (so taller than wide). 
I'll try figuring out the custom way, but would be nice to have them in the predefined list.
Agreed, the custom way doesn't really work and it's visually very messy, for those of us with large vertical or ultra widescreen real estate the ability to split 3x2 or 3x3 would be incredibly useful.
I cannot see the above control panels in bettersnaptool, only 'create from current as template' and besides it needs to work for multiple monitors. Any plans to integrate this feature?
Top Left 3rd
Top Middle 3rd
Top Right 3rd
Middle left 3rd
Middle middle 3rd
Middle right 3rd
Bottom left 3rd
Bottom middle 3rd
Bottom right 3rd