Hello helpmeharman. The problems you have are the result of the way Bituminous coal burns.
Most Bituminous coal has lots of 'volitiles' in it.. this is the burnable product that we see as that gray/black smoke that pours out of the coal when it is first heated..this is the volitiles boiling out of the coal.. To burn these volitiles you need HOT fresh [oxygen rich] air added above the fire in the area of the smoke.. without this added hot air, the volitiles remain as soot and smoke,, and will clog the heat exchanger in the top back section of your SF250. You can open the spinner knobs on the loading door a very little amount, this might help burn off some of the soot and smoke..But these over-the-fire air vents should be open only for the first say 20-30 minutes after fresh coal is added to the fire, after this time, close them so the only air getting to the fire comes through the ashpan door's air control spinner knob.
Each vein and mine of Bituminous coal is different,, some have more volitiles than others.. do you have a different source for coal that might have less volitile content??
Is your stove located on the main floor or in the basement?? If on the main floor, you have an effective chimney of only about 12-14', that is marginal for burning a coal that needs lots of air to burn well.
Your Stokermatic you mentioned heats the coal as it reaches the bottom of the burn area [feeds from the bottom]. As the coal is heated, the volitiles are pushed through the hot coal be and burned very well, this usually eliminates the soot problems from high volitles coal.. In the Bit forum, read the thread about combustion air to the Prill stoker.. this will help explain some of the fuel/volitiles/ air relationships.
Since this is really a Bituminous coal burning issue, I'm moving this to the Bituminous forum.. maybe the Bitum guys out west can help with a different coal source. or burning suggestions.