I'm glad that I'm not the only one that suffers this ailment. LOL. I often pick what look like pieces of partially burned coal out of the bucket and see if they will break or not. If they will not, I frown, just 'knowing" that they could have somehow been forced to give me another btu.
Yiour bed looks very juch like that of a KAA-2's. Fyi, the grates on mine [bought new] have a couple/three rows of holes at the end that were hand drilled [not too straight]. So, I trust that at some point, Keystoker felt that adding the holes was best.
There are many threads here on the subject. I have reluctantly come to the point that I agree that more than the idea amount of air might make the ash look better, but it is wasting heat by blowing it up the flue. However, I had not thought about what you are doing about here. You could be dispersing the same amount of air in a better pattern.
On a related subject, I have read opinion here that one will always see some unburned coal when using a flat bed. I am still planning to tilt my bed down at 5* or so. It seems to me that if the coal was less densely packed, the coal might "see" more air, with the same air amount. The coal might move in bigger jumps with the bed tilted down, which *might* allow it to be less dense. Here's a thread on that, in case you haven't seen it; flat bed [KAA2] vs sloped bed stokers
fwiw, I may try to fashion a 3 sided "adapter" with wedge shaped sides just to try it. If in case it did work [or I thought that it did LOL], the mounting flange could be cut off and re-welded for a permanent down angle..