With the same 1/4" opening in your air control, you will get roughly double the amount of air feeding your coal fire, this will increase the burn rate, increase the heat in the stove. The increased heat in the stove is being drawn up the chimney by twice the draft [suction], so the temperature of the flue goes way up.[more draft], More very hot air from the stove is going up the chimney, the fuel is burning faster, and the stove may not even be hotter, the heat may be just going up the chimney
This idea proves a point I have recognized and mentioned for a few years here. (Maybe a little off topic )
Let's assume I have small hand fired stove. I have this puppy really fired to produce the heat I need. My hot stove air is 300F but my TRUE flue temps are even hotter at 350F. My draft is set at .05" (I often read guys stating very hot flue temps. Very hot to me is over 250F )
Now let's assume I have a larger stove capable of creating the necessary btu's to create the heat I need. My stove hot air is a mere 200F and my true flue temp is 175F. and draft is .05" My fire is at a mere simmer and not blazing red as in the first scenario. My coal usage is at the minimum for this unit.
Pound for pound, the 2nd larger stove is using less fuel than the 1st unit to make the same amount of heat in a period of time.
My point, hand fired stoves are designed to fire at a simmer, not at a blazing hot fire. Not at a high rate as I have read from others on this list. They are not as adjustable as folks make them out to be unless of course you have no regard for the amount of fuel use or the amount of times a day you tend to it.