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I just use a piece of aluminum flexible dryer vent and slide it over my stack. It raises the stack about 15". Handy to have on those days will little or no breeze. I slip it on and off as I feel I need too.
First of all I love your back light. I bet you have no trouble at all seeing if the smoke if still flowing, from inside the house at night.
For such a short chamber, 24" tall X 4" Dia. chimney seems a little too much to me, but I'm no expert. Not even close.
Look in the "Smoker Build" forum. They can help you figure it out.
I just use a length of dryer vent that extends my stack about 12" -15" above the normal stack. I slide it on and off as I feel I need to.
On really calm days, I'll stretch it out a bit more to help the draft. Don't know if it helps or not, but it makes me think I am doing something anyways. What I have works for me, but I don't have your 50/50.
Outside stack extension is laying on the left of smoker. I just slip it onto the original stack. It fits snug.
I always bend it in the same direction the wind is blowing so it doesn't blow back down the stack.