You really can't load half as much coal.. unless you figure out a way to block half the firebox and grates.. Coal likes a deep fire, control the heat output with the spinner knob.. But don't try burning a shallow fire, you won't get less heat.. Heat output is determined by the area of the fire, not the depth [quantity of coal].
But there is a 'catch 22' with hand feed stoves.. you HAVE to have a fair amount of heat leaving the stove to keep the chimney warm to provide draft to pull air through the bed of coal.. too little air= too little heat= too little draft= fire going out..
So with hand feed stoves,, you have to use your 'windowstats' in warmer weather.. this of course depends on how much heat your particular chimney needs to maintain enough draft to maintain the fire..
Never fear,, cold weather is on the way..