Ratios are not always accurate in combat math. For instance, arithmetically, we could calculate the new troops that the RCC needed as:

Old GK forces: 754
Needed RCC force: 4063

New GK forces: 754 + 1000 = 1754
Needed RCC force: 4063 + 1000 = 5063

This new number is well below the RCC's current forces. Problem is, whatever math we use, except mathamancy, we can't fully represent the situation at hand. Here's why:

1.Tactics
2.Unkown force multipliers
3.As mentioned by others, disparity in unit power
4.Charlie

1)This comic has shown time and again that poor tactics can not be made up for with numbers. That Ansom isn't using any at the moment is far more damning than not outnumbering Parson by 'enough'.
2)They're all over the place, and we only know a handful. The tunnel battle illustrated just how crucial they are.
3)Parson has added 1k low-level zombies. He's lost dozens of dwagons, possibly all of them, as far as he is concerned. Those dwagons were probably more useful to him than those zombies, yet numerically, there were less of them.
4)Charlie is a big unknown, and can change the tide of this battle completely on his own.

All that said, I enjoyed reading your analysis because it was well researched in regards to the factual numbers concerning each side. In the future, approach your math from multiple venues to see how different maths affect your predictions. Statistics is impossible to apply from a reader's standpoint(we lack a sample size adequate for it), but I'm sure there are one or two others that could work.