I can't find it anywhere, bit I think you want either a) other than zero in those fields on both of the simul-ring devices, or b) set value in both devices to 127.
In hindsight, I don't know why I thought you want different values, an an option c) try a test of having one set to 127 and another to 126.
Also try searching for "XMPP Priority" (search full internet not just
obihai.com). An FYI, simul-ring does work, based on several people on here having reported using it successfully.
Maybe someone else will chime in here.