I suspect you'll always find the upper layer bricks are smaller than the lower layer bricks in any given pyramid (and possibly in most given ancient constructions.) In part, it's so the rise is nice and smooth (something I suspect they figured out with the brick constructions) and in part it's to minimize problems on the build.

It's more efficient to put the smaller stones on top. It's also faster to quarry them -- but you don't wan the little guys on the bottom because the weight on top will crush them.

I rather imagine ol' Imhotep figured this one out after some embarrassing mastaba failures of previous history.

-- Byrd
Moderator, Hall of Ma'at