Coincident & Concentric mates together...?

Hi all,

In the attached subassembly, I'm trying to make the flat back face of "SUBASSEMBLY Thermostat" be coincident, as well as concentric, with the nearby gray extrusion "Therm Face". However, I've already added the

(...seemingly, haha) appropriate mates, and all I get is errors. Anyone have any idea what I may have done incorrectly, and/or what I could do to get these components properly mated?

Any help is appreciated !

Thanks in advance,

SolidworksModeling And Assemblies