"The second study, by Robin Canup at the Southwest Research Institute in Boulder, also backs the impact theory, but she reckons that the Earth and the planet that hit it were each around half of the Earth's current mass."
The maths doesn't work for this unless her assumption of each Proto-Eath and Theia has a tolerance range of half a moon each, which is a kinda hefty tolerance...
@ Local G
Perhaps the matter that makes up the numerous moons coalesced seperately to the gas giants and then got dragged into orbit around them as the big fellas were on their little trek around the sun