For an explanation of the formulas, go to this page and scroll to the bottom of the page.
The last two explanations will answer your question. They are brief, to-the-point, and make use of the term "relative" in discussing boat performance. "The intention is to provide a means to compare the motion comfort of vessels of similar type and size, not to compare that of a Lightning class sloop with that of a husky 50 foot ketch." People seem to forget that point. It should be noted that I do not dismiss Jeff's example of lead weight at the end of a mast, but while that isn't gonna happen, some cruisers can get into trouble by counting on a given capsize ratio, only to upset this number by stacking their boat high and deep with stuff over time. This will raise the center-of-gravity and affect the boat performance. For example, the greater weight may actually help motion comfort, but it could also cause the boat to wallow to excess when it should be recovering. This can set up other problems. Balance is important. As Mr. Brewer states, these formulas are relative (not absolute), but they do help with general comparisons.
Also, to be fair, Jeff's boat (Farr 38, isn't it?...and I'm not dissing it) comes in at 2.19 capsize ratio, and 17.81 motion comfort. :-P
Still, gotta take issue with the thousand pounds at the top of the mast. It would improve motion comfort. As I touched on this already, the weight would slow the boat reaction to the sea, causing a slow wallowing recovery. While not favorable to survival, it would still act within the motion comfort idea, which is a measure of damping of directional change...in a relative sense it would be more comfortable, til it flipped over or was swamped due to excessive wallowing. As stated, balance is important. However, the formulas were developed with the understanding that would take into account the normal basic layout of a sailboat. Having 1,000lbs at the top of the mast is not reasonable, nor realistic. That example is akin to comparing the speed capabilities of two boats, but having one drag anchor on the bottom, and the other is not. Point being, any formula can be discredited when unrealistic data is plugged in.
Similarly, the capsize screen is simply a formula used to compare beam and displacement (nothing else), and how the two interact to dictate characteristics of a boat in a seaway. Again, nobody considers the handling characteristics of a boat with a top-heavy mast. Why should they? The formula simply is used to get an idea of how a given amount of beam to displacement will affect handling. Too much here, too little there and you get stablility issues, or more stability than needed at the cost of speed/efficiency. Whether those stability issues are controllable (in a given situation...coastal vs bluewater), perhaps even beneficial, is something that has to be fleshed out. That's when you plug in other factors. Look at boat design. They all start out the same way....hull first, and nowhere do they have a sign hanging saying to factor in a top-heavy mast. You start with the basics, then adjust for an intended use, and compensate (or should I say compromise..."All boats are a compromise..." for excessive good/bad characteristics as they creep in.
It is safe to say that no formula can fully predict boat characteristics, but is is wrong to say these formulas, and others do not offer useful information.