My inexperienced idea would be to open your shutter a little more. I think I remember you saying you had a low draft when it was half open, so maybe you can find a happy medium between that and where you are now. If your draft can handle the extra air flow, great!!!, your coal will burn more efficiently and hotter. More air = more burn. While adjusting you shutter, you should see an almost immediate response from your manometer, so at least you don't have to sit around waiting too much.
Even though I have a good draft (knock on wood), right now my shutter is less than a quarter open. Once it gets consistently colder, I will open it up more.
I am not sure how high a draft is too high. I would try to stick with Keystoker's recommendation. They have their reasons for wanting a .025 on their kokers.