First, memory-beta concerns the Star Trek novels, none of which are canon. All information on Borg cubes that came from a novel is also not canon.
Second, memory-beta claims that a baby "tactical" cube is 3,040 metres. You yourself posted a link to a image of Voyager (132 metres max width) adjacent to a baby cube. How can you reconcile the 3,040 metre figure, with the linked image?
Star Trek Online is a internet fansite, they can make up anything they want to play their little wargames. It's all fan fiction, some of it is interesting, but non-canon.
Voyager is closer to the camera than the cube.
I have given you references, and maybe those references are not to your liking, but they are references none the less. Memory Alpha didn't mention its size or how it compares to a normal cube.
Your assertion that a Class 4 Tactical Cube is a baby cube, needs to be proven.
The episode Unimatrix Zero, made it obvious to the audience that this was a "bad ass" version of a borg cube. All links I can find say it is a "bad ass" version of a normal borg cube.
You are the only person on this planet claiming it is a "baby cube".
If you have a reference, even a non cannon reference, I'd like to see it. Other wise, I am going to assume that I am correct, until I see something other than your own personal opinion, to contradict me.