I've done this twice. The first time, less than half in the carton hatched. The second time I had 30 eggs in the bator at lock down, all were from my own flock, and only used 1 carton for 12 of the 30 eggs. All but 2 hatched from just laying on their sides and only 3 hatched in the carton. I've noticed it is much more difficult for them to get out of the vertical egg and if you think about it... the eggs lay on their side under a hen, not on their peak.
And I did cut it down and cut out the bottom to allow circulation.
I won't use a carton again for hatching, sure they bang around laying on their sides, but I've only noticed that it would coax others out and never saw an egg cracked due to rolling.