The horizontals can be ignored as they do not contribute to the convection.
They would not be horizontal, everything contributes toward convection.
How would the top 1/3rd of the system get hot if the water is not leaving the stove?
If its leaving the stove what replaces it?
Water being heated by the boiler.
Where is that water going?
Into the circuit and starts cooling.
This will continue, it wont just stop
Why have dunsley put that vertical loop in?
To start convection even in the event of a powerfailure, not to see how long the aav will last before it turns into a steam whistle.
As soon as the water leaves the stove it is cooling.
The hottest part of a system is not the top pipework, its in the boiler.
As I posted before, why do you drop a return pipe down low before you connect to a solid fuel appliance?
To help convection.