If you have a dozen good guys, but four of them are the protagonists and the other six are more in the background, it's not that hard to skew the pagetime of each character towards those that are more important to the plot.
But if all twelve characters are equally important (like one of those superhero unions or something), then I've found things seem to get difficult. Obviously the characters that are actors more than observers get more pagetime simply due to being more involved in the plot, but I still feel like the less-involved are being shafted a bit, especially as the characters I tend to favour wind up being used more often. So far the most common character has ~11% of the paragraphs while the least common two have ~4% each (with ~14% of the paragraphs being attributed to no one).
Is it reasonable at all to expect better distribution of spotlight? Aside from breaking the cast into subgroups and focusing on one group at a time (which is planned), is there a feasible way to divert subconscious bias? How many simultaneous protagonists is too much?