Keystoker 90K flame height

I've asked a couple friends and I am getting mixed results so I finally decided to get over my embarrassment due to lack of knowledge and ask the forum group.
Situation...as my signature states, I am a "Newbie" to this coal burning. Keystoker 90K BTU is set at factory settings and when it is calling for heat, the flames are always touching the ceiling of the chamber. One friend says that the flames should not be that high being that it is bad for the metal. Another states that that is normal. The guy I bought it from stated that he has seen some Keystokers produce flames that high.
So my question is...for best heat with efficiency, how high should those wonderful flames be?

Thanks in advance and thanks to all involved in this forum. Great info!

Our keystoker 90K running full throttle, the flames would touch the top of the stove. As long you are not pushing hot coals off the end of the grates, you should be fine. I have been running it for 3 years without any problems. I have had the sides get upwards of 400-500 degrees (with magnetic Thermometer).

Your convection blower takes the air across the top of the stove, so it will always be washing the metal of heat into the room.

Not sure if adjusting the combustion blower (covering the inlet) would help decrease the flame height? Never tried it. That will affect your draft a bit and make sure your fire doesn't go out either.

I get flames against the top of my Keystoker REAL easy. I have an older model and the design is somewhat different in the internal construction. The heat exchanger comes pretty close over top of the stoker and it's an angled plate. Hard to explain without a good picture. At any rate, it's not that far above the fuel bed, and with any decent amount of stoking, the flames are hitting that plate, which is also cooled by the convection blower.

So far, in the 10 or 12 years it's been around (I'm a first year owner of it), no problems at all from the stove body itself, even with some serious neglect due to lack of regular cleaning of the internal guts and direct vent unit.

mines the same way. with a 5" to 6" bed burning it's hitting the top. but it bounces around and not really hitting one spot all the time. if that makes sence.

Thanks for the info guys. Much appreciated.