You can also let the setModuleHeaders function of the ServicesFramework to set the headers for you:

self.getIndividualsInPositions = function (pageNumber, pageSize, positionList) {
            self.LoadingData(true);
            $.ajax({
                type: "POST",
                cache: false,
                url: baseServicepath + "GetIndividualsInPositions",
                beforeSend: _sf.setModuleHeaders,
                data: {
                    PositionList: positionList,
                    WhereClause: self.WhereClauseFilter(),
                    OnlyIncludedInDirectory: !self.TabState[3].IncludeNotInDirectory(),
                    PageIndex: pageNumber - 1,
                    PageSize: pageSize
                }
            }).done(function (result) { . . .

In your services controller methods, the ModuleID, TabID, PortalID, etc.  will be available on the ActiveModule object.

As for the SupportedModules attribute, I initially had the same problems with this until I realized that the value should be the name of the project's DesktopModules folder, not the project's namespace:

// Path is DesktopModules/WESNet_FamilyDirectory/API/FamilyDirectoryServices/{action}
    [SupportedModules("WESNet_FamilyDirectory")]
    [DnnModuleAuthorize(AccessLevel = SecurityAccessLevel.View)]
    public class FamilyDirectoryServicesController : DnnApiController
    {