staves won't fit on page
I've thinned my bottom page margin to the point at which it's almost nonexistent and set the music bottom margin to straight zero--yet in the attached score, it makes no difference on the first two pages. There is clearly enough room for at least one more stave at the bottom of each page--just look at all the empty space down there. And compare the third page, where all the space is filled up. I can't figure out what's wrong on the first two pages. Can anyone tell me?