The mind as a physical field? Yes, I agree with you, if there is no way to detect a mental field by experiment, it is all no longer an empirical thing, but just purely philosophical or simply speculative.
I thought of the field as a genus, of which there are many species, like the electromagnetic field and perhaps also our mental. Therefore, I thought a distinction of the two would be insignificant.
One of my presuppositions beside naturalism was also that our mind moves our body. There would be a direct proof for the causal-physical effectiveness of the mental of our mind, because we experience it so.