Alaska Liberty Stove

I have a question. I started using my stove 3 days ago. And for some reason when the hopper is 1/4 full it does not heat as well as when the is 1/2 or more. Any thoughts

If it's a stoker, the hopper shouldn't have anything to do with heat output, it will feed what it needs, depending on the settings. the heat output is dependent on the Fire size and feed rate.

Do you have a rheostat or thermostat for heat control?

I understand that the hopper just stores the coal. But the weight of the coal at the bottom is very
heavy in hopper 50% or more and less around 25% or less