@maxdancona,
Well, with two coins there are just four possibilities, two of which involve results of half heads and half tails (one of each), in which case the odds of getting an equal number of heads and tails are 1/2. But if you increase the number of coins to four, then of the sixteen possibilities, six involve equal numbers of heads and tails; so the odds are 6/16, which are less than even odds. (The easy way to prove this is to print out the numbers from 0 to 15 in binary, then count how many of the sixteen possibilities have equal numbers of heads and tails.) Inferentially, the more coins you add (doubling each time), the lower the odds of getting an equal number of heads and tails.
I'll accept your probability of 22.5% in the case of 12 coins as a stipulation, without calculating it.
That said, I still say that probability is a quantity associated with a set of events, and that where events are causally independent of each other, the selection of a particular grouping of events, constituting a "set" for purposes of statistical analysis, is a subjective, observer dependent act, which in turn determines the probability associated with the event set.
Consider a set of 12 coin flipping machines. Each machine has a single coin; and each machine makes a single flip. Each flip constitutes an "event". Neither the spatial nor the temporal proximity of these events is specified. All twelve machines could be in the same room, executing their flips simultaneously. They could be in the same room, with their flips separated by minutes, days, or years. They could be scattered across the world, conducting their flips simultaneously. They could be scattered across the world, conducting their flips at different times.
There may be a number of other such coin flip machines. The number of other machines is not specified, and may not be known or knowable. The spatio-temporal relations of the coin flips of these additional machines, whether to each other or to the original dozen under consideration, is not specified. These additional machines do not enter into this hypothetical, except to flesh out the boundary conditions a bit.
The coin flip of each machine is causally independent of the coin flips of the others.
First, note that the selection of 12 particular machines, out of a possible myriad such machines, is a subjective, observer dependent act.
As it so happens, among our 12 machines, half toss "heads" and half toss "tails". You specified the probability of this result as 22.5%, which is between 1/4 and 1/5.
However, if we define as a "set" only the six that flipped heads, and ask what the probability is of flipping six heads with them, the answer is 1/64.
If we define as a set the six machines that tossed tails, the probability of six tails is also 1/64.
If we ask what is the probability of one set of six machines tossing six heads, with another set of six machines tossing six tails, you've said that the probability is 1/4096, which is the product of the two individual probabilities, (1/64) * (1/64).
Yet, we've already stipulated that the probability of getting half heads and half tails from the same 12 machines is much greater, between 1/4 and 1/5, or specifically 22.5%.