"Position statement" = collective statement by a group of experts on a topic. "Encompassing field" = group of medical experts who study a larger body of knowledge that includes CFS/ME as a subset.

Like, in physics there is a big field of people who study dark matter, with subfields who specializes in certain (often mutually exclusive) hypotheses about what dark matter is made of, e.g., WIMPs, axions, etc. If I wanted to know whether a new hypothesis about dark matter was plausible, I'd want to hear what all the dark matter specialists thought, not just people who already committed to studying that particular hypothesis.