Magnum Countryside only burns right with ash pan cracked open

[huntingbuck101]

I have about 2 tons threw my countryside insert and it will burn fine #1 threw 3 as long as the draft is all the way out and it been this way since new. Now that it's colder out I need heat setting 4 or 5 but it fills the pot full of pellets and unburnt pellets. This makes my stir rod glow orange and expand and makes the part where it goes threw the bushing creek real bad. With the ash pan out 1/4 to 1/2" it runs great, pellets burn low in the pot and stir rod is quiet. I have a OAK and it is clear, stove is clean, exhaust is clean. I put a fan that pulls 25 CFM more air on the exhaust blower, didn't help. Dealer was out for 5 1/2 hours and cant fix it. It just seams like the air intake tube that comes in under the burn pot and above the ash pan needs to be bigger to allow more air and when I open the ash pan it gets the air it needs.