I have beeen burning a Stratford SC100 ( this model is slightly larger than yours, it has three shaker grates compared to the two in your SC 75) for 6 seasons now. I love mine, sure it's alot easier to hit a button on the wall but that button doesn't work when the power fails!! Coal is also way cheaper, even with the price increases, $80-$90/ton, in my six seasons. Wood is great also if you don't mind the work. Glad to hear you got your firing or lack of worked out. I have learned that the gaskets have to be kept in good shape to keep a tight seal or you will have the troubles you posted. I replace mine every two years or sooner if needed. The only reason I could come up with the ashpan being like it is would be to allow it it slide back in while scooping (sort of) the spilled ash back in as mentioned by other posters. I fabricated a pan with a back on it which helped a little with spilling ash but the daming effect it created pushing ash to the back wasn't worth it. I went back to the stock pan and just have to be careful getting to and out the door to empty it. I did fabricate a cover for those windy days ( it's flat with a bend to match the angle at the back of the pan). I also find that I ocasionally have to shovel out the spilled ash at the back of the stove. The door constuction??????????? Only thing that even remotely makes sense to me is to try and keep one from over-firing the stove, it's not fool proof though, you can over-fire with the ash pan door cracked open as well........trust me! The door constructions biggest drawback is when tending to the ocasional jammed grate, which always will occur when you are burning the stove hot (Murphy's Law) and you have to poke up from the bottom with the ash pan removed.
I have learned that the harder the coal the better it seems to burn,but I'm no expert! I also have a second identical stove for back up! I purchased both of mine used. I'm lucky to have a dealer about 10 miles away that still carries parts for these stoves. Last I knew they were not being imported any longer. One thing I do as a rule is keep a spare glass (Ceramic) on hand with the flat gasket installed. Learned this lesson when I got the " What happens if the glass in the door breaks while the fire is burning" phone call!!
Of course the dog got blamed for it
I typically will burn wood to start and end the seasons. Don't know if any of this helps....hope so! Fire away if you have any other ???? Joe