Well, you have to set it with a draft gauge, If it's on 10 and wide open, doesn't sound correct. It could be stuck open, does it move freely, sometimes if it goes to far, it can stick.
You really need to calibrate it with a draft gauge (manometer) to accurately set it. Mine in only on the 2-4 setting and maintains .03-.04 most of the time.
Are you using the Field Controls RC type baro? The numers indicate the Draft 2 = -.02, 4 = -.04 etc....These are ONLY approx.
If you are, the weight should be on the RIGHT for veritcal mounting.
Most stoker stoves should run the -.02 to -.04 range.