In November, I installed a Kodiak with a hopper, and I don't have any problems. I didn't get the screen with mine. I was under the impression that the screen was to put in if you wanted to burn wood with the door open- fireplace style. Did the dealer tell you to put it in with coal? Basically, the hopper allows you to add more coal for a longer burn time. I don't always fill mine all the way up, because I'm usually back home to tend the fire often enough. But I have filled it on occasion, and had no problems. You still need to shake down the ashes every 12-14 hours, or the fire will start smothering itself, or at least mine does. I use nut size coal. Is that what you have?
The bottom edge of the hopper is actually a couple inches below the top of the bricks, and tends to keep the coal bed deeper in the center. Without the hopper, you should be able to fill it to the top of the bricks, and taper it down slightly in front, to keep it below the door and glass. ( I assume you are referring to the front door when you said you fill it to the "load "door. If you are filling it up to the top loader door, that's way too much! ) Don't fill it above the bricks without the hopper to contain the coal. Again, I'm no expert, but I don't think the screen should be in there when burning coal. Maybe someone else can elaborate ?
Maybe you have too much draft? What size & height is your chimney? Do you have a barometric damper to regulate the draft?