Hi There, just stumbled upon your smoky stove issue - had the same issue myself and did some research- discovered that horizontal flues are the enemy when it comes to getting good draft in a chimney -any horizontal flue over 12 inches/300mm is a big no-no and should be kept to min length as possible. This is compounded by the fact that modern stoves are super efficient at containing the heat in the firebox (my own is measured 75%) this means less heat to the chimney flue which in turn means slower smoke movement, slower to get to the 35 degrees operating temp for capillary heat movement(draft) up the chimney.
How to resolve: try get rid of horizontals and harsh 90 degree bends, they are trapping slow moving smoke and its easier for the smoke to flow into the room, introduce 45 degree joints and diagonal/vertical flues from the stove. This will allow smoke to flow/escape upwards. Also insulation helps greatly as the chimney gets to operating temp more quickly and retains heat (also prevents condensation and premature aging of flue liner)
Hope this helps cheers