I think what you are really asking is can the region of fusion be controlled relative to the Anode? Obviously, the plasmoid doesn’t form until the filament passes thru the toroidal magnet, which imparts the rotation force to the plasma. What is most important to me is when the collapsing magnetic field will allow for X-ray suppression from injection of electrons. If collapse occurs too close to the magnet and anode, the rotational force from the magnet may not be enough to form a stable plasmoid. The collapse time is a function of ionization and temperature of the plasma. I don’t have an equation for you but Dr Lerner may have.