Simulation Distance in Realms keeps reverting to 4 chunks

I just paid for 6 months for my first foray into hosting a realm, and I'm trying to set the Simulation Distance to 10 chunks. Every time I save the game, however, and go into the save to edit the settings, the game is set to 4 chunks.

I also notice this with my hopper furnace in my mine, as when I'm at the end of a branch less than 100 blocks away, the furnace will stop smelting.

Is Simulation Distance not available in Realms? I can't find a decent answer anywhere, only speculation, some of it contradictory.