OData batching seems to be inconsistent

My App is essentially a hybrid much like say sharepoint, in which I have a combination of related products that are all pulled together.
The net result though is that I have mapped Odata routes like this ...

services.AddControllers()
    .AddOData(opt =>
    {
        opt.RouteOptions.EnableQualifiedOperationCall = false;
        opt.EnableAttributeRouting = true;
        opt.Expand().Count().Filter().Select().OrderBy().SetMaxTop(1000);
        opt.AddRouteComponents($"/Api/Core", new CoreModelBuilder().Build().EDMModel);
    });

services.AddControllers()
    .AddOData(opt =>
    {
        opt.RouteOptions.EnableQualifiedOperationCall = false;
        opt.EnableAttributeRouting = true;
        opt.Expand().Count().Filter().Select().OrderBy().SetMaxTop(1000);
        opt.AddRouteComponents($"/Api/B2B", new B2BModelBuilder().Build().EDMModel);
    });

In order to test this I've built an "ApiClient" class in my front end code which defaults to being setup with a base url like this ...

var api = new ApiClient("~/Api/");

When I want to perform batch operations on the "core model" endpoints I seem to be required to use batching from specifying B2B as the root ...

I was thinking that expecting the app root or at the very least ~/Api/ which in this example would mean posting like ...

   await api.post("$batch", data);

... would make more sense, but I think it at least works (I guess, despite me not understanding the logic here)

Then there's this ...

... for some reason I seem to be finding a lot of requests that only work when not batched, how do I debug this?

Start with the two AddOData configurations and their /Api/Core and /Api/B2B route components, then reproduce the requests through the ApiClient using both batched and unbatched forms. Trace the batch endpoint and the requests shown in the report; done means the routing behavior is explained and the inconsistent requests have a confirmed, reproducible outcome.