The spawn rate for ghasts in the nether seems much higher than pre 0.16.0. Ghasts are so common that, in trying to shoot the player, they instead shoot another ghast that has gotten in the way. Even in very small pockets of space, I frequently encounter multiple ghasts. I've seen as many as 5 ghasts pinned in a small pocket that was 3 blocks tall. It's not uncommon to see ghasts spawn into the nether in a space that is too small and then quickly die. Just standing in a tight passage in the netherack, one can regularly hear ghasts cry and die off, presumably from spawning into a too tight pocket that is out of sight but still within hearing range.