I agree it is not a problem with your current design. The Line of Thrust (“LT”) in an arch follows the inverted shape the corresponding catenary curve. That is, if you freely suspended a length of chain from the center points of the angled buttresses on top of your solders, the LT through the arch would follow this same (inverted) curve. The closer you keep the LT to the center of the voussoirs, the more stable the arch. As the LT moves away from the center, it creates tensile stress on the opposite side. That is what Jeff noted as “outward force” on his drawing in Response 77 – you can see that the inverted catenary curve would be well inside of that point creating tensile stress there. As long as the LT is within the center 1/3 of the thickness of the arch, you should be fine. My guess is that the truncated ellipse fairly closely approximates a catenary arch.
I think your drawing in Response 76 is incorrect in a couple ways. First, the LT, or “Force” as you called it, is independent of the shape of the dome arch. As noted above, it is a function of the corresponding catenary curve. Second, the force is not going to be directed into the solider as indicated. My guess is that the LT vector will be on the opposite side of the solider. I think this is important as it what likely necessitates a minimum of two bands (above and below the mortar line on top of the soldiers.
The solider is part of the arch. As you can see below, the LT exits the arch somewhere near the top of the solider. Clearly, this creates an extremely unstable condition. The Thrust vector is the resultant force of the Horizontal Thrust and Weight vectors. The soldiers will bear all the weight of the dome, but the direction of the Thrust vector is not orthogonal to the long axis of the brick, hence the need for reinforcement in the form of the bands or some other reinforcement.