Hitzer 82 Restrictor Plate

I think I found the limit the restrictor plate will let me reach. I've been wondering why my stove won't go above 400f on the thermometer, and I think it is because of the plate. If I move my dial anywhere above 12.5 or 13 (max 15) it doesnt seem to matter because the restrictor maxes out the input air. Last year I was using different coal and dealer and I think that could also be why I am having trouble getting the higher temp with the same amount of air. Currently I am using superior red ash, and I haven't heard of other people having problems with superior. I just shook a ton of ash out of the ashpan, and even shook until I am getting a fair amount of red embers , and red all through the grates, so I know it isnt ash buildup. After I did the shaking I added about 40 lbs of fresh superior to it. The only other thing that could at most be the culprit is that the gradation seems a bit slanted on the smaller size of nut, and not the larger pieces.

I believe the plate on my 82 UL is held in by one screw which also holds the air regulator flapper. I don't see it being easy or safe removal with a running stove.

Who has adjusted there restrictor or removed it? Is it safe to do it? I am thinking that an "adjustment" maybe in order, but how much is the question. Maybe figure out how much "air flow" area there is now, and increase it by 10%-20% to increase heat output by that much ? I would just grind/cut some metal off of the existing plate.

Anyone do any yearly maintenance to there 82 that may affect heat output? I didnt do any maintenace to my unit between seasons. The draft seems to be reallly good.