So I went back to replay level 80 without a team of 5 Carsons and got the gates of hell layout. I tried to play it and got killed on turn 2 when all the small pigs attacked. I got a similar layout on 78 or 79 but had no issues because my team power was over 137k. This time, I was testing it with a much lower team power and was killed immediately (verifying that the health of boosted birds is also increased). Well I wanted to try something else but was out of energy. I had 8 energy left so I paid the 4 gems to reenter. When it loaded, lo and behold, my layout had changed completely: it was no longer gates of hell. I have no idea if my paying the single gem reentry fee made the game change layouts to an easier one, but I paid the fee and it did. I did not pay 100 gems to refill my energy, just the single reentry fee. Maybe some of you other guys can test this and see if paying the single reentry gems for the event stages makes the layout change like it did for me.