A few more QX design factors can be extracted by considering the implications of the nature of the KERR stimulus control mechanism.
Because the KERR effect is mediated by an electrostatic field, the material that the QX is made from must allow that field to get through the reactor structure and into the fuel. Therefore the structural material must be a non metal. Rossi might use non metals throughout the QX structure to avoid field absorption and to enable better control of that field.
Many QX tubes can be controlled by one all encompassing electrostatic field. A direct wire connection does not need to be made to each QX tube.