I have a Lopi 1750 free standing stove. I close my air 3/4 to 7/8 on every reload and never have brown soot on my glass. I think you will find that your wood is a bit high in moisture. If i ran my air half open on 3 or 4 hardwood splits I think I'd be worried about my stove melting. I regularly let the stove burn out overnight and go to bed with the air almost all the way closed with no soot on the glass. The airwash on these stoves is pretty good.
Good to know. Thanks! I did do the dollar bill test this AM. Could not easily pull it out, so moisture content and wood type could be playing a role.