The most likely cause is that the sensors are not exactly the same active size, even if both are marketed as “2/3-inch.” That format name is only a class, and real sensor dimensions can differ slightly. A different active sensor area changes the field of view, so you must move the camera to match framing.

Because you are using the same lens, the lens projects the same image circle. If one sensor captures a slightly larger or smaller portion of that image, the framing changes.

A second possibility is measurement reference: if you measured from the camera body or tripod mount instead of the actual sensor plane, body design differences could make the camera appear to need a different distance.

A large sensor-plane offset is less likely, because a big shift would usually also create focus problems, including at infinity.

So in practice, don’t rely on the quoted “2/3-inch” format alone for mechanical design. Check the exact active sensor dimensions and the true sensor-plane position for each camera model.