To measure is to know.
Helped someone with their stoker last year with a similar problem. In their case the stove was a bit too close to the wall and they didn't have enough room to fully adjust their draft.
We measured with Manometer, couldn't get the setting we needed, moved the stove 6 inches and set draft to the proper setting and viola!
I checked with them a few weeks ago and it has been burning great ever since.
The key here is you want to SET the draft to spec, not just check the draft