The Sigma Foveon's have a crop factor of 1.7 IIRC, smaller than APS-C so certainly no APS-H ....
And then there is at least one existing Sigma for L mount [which is FF], plus the persistent hope for the Sigma FFF (Full Frame Foveon).
Nikon 1 and Pentax Q are small sensored ILC's
To me this shows that the format is not a very good distinguishing point to base the organization of the forum on. I also don't see what people might want to discuss on the FF or APS-C level. We all know our equivalence don't we, some even got the t-shirt.
What is more useful IMO is a categorization based on lens mount: for instance all Nikon Z lenses and adapters can be used on all Nikon Z bodies, independent of the sensor size