I tried to run some tests in a controlled environment. But I would need to sit for something like 40 hours taking notes before I would be confident of my observations. But right now, however insufficient data I have, it seems that it's most likely the size, and not the strength. But then again, my sample is so small that I might be wrong after all.
Cross shots - I just don't know. I saw it too often to just call them a bug But I wouldn't put the probability of it happening higher than 2-3%, and most likely it's smaller than 1%. Maybe it gets higher under some special circumstances I haven't tested. Personally, I very much doubt it.
That's an interesting hypothesis I must say. Not that it's easy to check. You can never be quite sure that the merge bug did not happen in a given game.I would even go so far as to propose cross shots will only happen in games that have witnessed the merge bug or whatever the merge bug has morphed into now that the same person can be king of multiple civs at the same time. You will know if all manner of strange occurrances are happening in the game already.