Not sure, when it gets chilly again I'll have to do some more testing. While you have a flame there you could supplement the fuel tab with some tinder or kindling.

As it stands, you can store four of the esbit cubes inside a closed stove. There isn't enough room for more cubes, but there is enough room that each of the cubes could have been maybe 10-20% larger and fit inside snugly. I'd imagine that would have at least gotten it simmering in those conditions which is better.

My cubes are several years old though, maybe that made a difference