those little ones like you show above are tough to control. I find that you have to keep the ash cleanout mouth full of ashes, heaped with ashes & lay the cover in there so you have to press it down into place. that blocks a lot of air from sneaking in from under the cleanout cover.
next problem is the huge gap between the bottom of the loading door & the top of the cleanout cover, they pull a boatload of air in that gap & the stove just runs wild.
I've resorted to keeping a little pile of cold ashes on top of the cleanout cover & I just use my hand to sweep a berm of ash against the door to dam up the air gap.
that ember hearth is a way better stove.
