proper draft and chamber pressures on power burner

I was recently checking a powerflame burners combustion efficency - was 70%- this is on a 900,000 btu steam boiler. I,m a little uneasy about how much adjustment the combustion air took to get the efficency up to 79%. The one thing imm not sure of is what the combustion chamber pressure and the draft pressures should be, the draft adjustment damper was 100% open now 75% closed, I had positive.5"WC in the chamber and -.25 in the flue. dose this sound normal.