Why is there a bevel in the lentil arch?

We are wondering if the bevel in the lentil arch goes to the inside of the stove or faces out?

It definitely goes to the inside of the firebox. The bevel is to help combustion gases smoothly find their way up the throat.

For context for others, @dclaire is in the process of following our plans for a 48”x32” masonry heater with 3-sided heated bench. It would be fun to see some pictures of your progress Claire!