The figures are adjusted for population, so I don't see why size would affect the figures, and as the other poster said comparing recently joined Eastern European states with the US is not very useful as they are at a very different stage of development. If you break it down by states almost every US state has statistics far worse than
Western Europe, to which they should be fairly comparable.
There are lots of variables here, including varying gun ownership, gun control, and states like Switzerland show you can have ownership without high rates of killing (though they restrict ammo), but widespread private ownership for self-defence in the US does seem to correlate with high rates of homicide (inc. suicide), and other countries with tighter restrictions and a different attitude to guns have far lower rates of death associated with firearms.