Ok, if your fire is not burning all the way across, then you have either ash clogging your grates, or inadequate draft to pull enough air through the coal bed to get it hot enough.
How tall is your chimney? I think I see a thermometer on the flue pipe in the photo, what is it reading?
When you shake down your ash, do you see [looking through the ashpan door, ashpan removed] a red glow above ALL of the grate area?? I'll bet you have dark areas around the outside of your grates. What you need to do is to make a poker,, a piece of 1/4" or 5/16" ore even 3/8" round steel rod, bend a 90* 'L' on one end, giving you about a 4" leg. Then make a handle on the other end, you can just bend another 'L' on the other end, a different length just so you can hang on to the round steel poker.. Use this poker to jab up from the bottom, in the dark spots, betwwen the fingers of the grates. This will dislodge the ash that is not shaking down adequately. ONce you have the ash all out, you will have a fully burning coal bed, and have to cut back the air to the fire.
Again, how tall is your chimney? what is the draft reading below the baro?
Some stoves have more effective shaker grates than others, some are too effective. The brand and ash content of the coal makes a difference too. You are going through learning stage with your stove and chimney. Some folks have had to learn all over again how to burn and shake in the SAME stove, just when it is moved to a different chimney.. the whole system determines the burn/shake characteristics.
ONce you have the ash in the ash pan, add plenty of coal.. the coal needs to be as deep as possible, up to the top of the firebrick around the firebox. Coal likes a deep fire.