HoH's floor 21 is the first set of floors where the game knows you'll 100% be 70 in there. 11 you end up at like 57-68 unless you were acitvely farming.

Palace's case, it's actually floor 41 where you're confirmed for 60. So technically speaking, they should have made you start at 41 instead of 51.

Plus like others said, HoH is smaller. Like... 50% smaller.