Thread count increases dramatically regardless of maxConcurrentRequests

Here is my simple http triggered function app.
Function1.cs
``` c#
public class Function1
{
[FunctionName(nameof(Function1))]
public static async Task RunAsync(
[HttpTrigger("POST")]string body,
[Queue("myqueue")]ICollector queue,
[Blob("mycontainer/{rand-guid}")]CloudBlockBlob cbc,
ILogger logger
)
{
try
{
logger.LogWarning(new EventId(-1, "FunctionStart"), $"{body?.Length}");

if (body != null)
{
try
{
await cbc.UploadTextAsync(body);
}
finally
{
queue.Add(cbc.Name);
}
}

logger.LogWarning(new EventId(-1, "FunctionEnd"), $"{body?.Length}");
}
catch (Exception gex)
{
logger.LogError(new EventId(-1, "FunctionError"), gex, body);
}
}
}
```

host.json
``` json
{
"version": "2.0",
"functionTimeout": "00:05:00",
"healthMonitor": {
"enabled": true,
"healthCheckInterval": "00:00:10",
"healthCheckWindow": "00:02:00",
"healthCheckThreshold": 6,
"counterThreshold": 0.80
},
"extensions": {
"http": {
// the maximum number of outstanding requests that will be held at any given time. The default is unbounded (-1).
"maxOutstandingRequests": -1,
// the maximum number of http functions that will be executed in parallel. The default is unbounded (-1).
"maxConcurrentRequests": 5,
// The default is false.
"dynamicThrottlesEnabled": true
}
}
}
```
In my opinion, the thread count should depend on the `maxConcurrentRequests` .
But it would go up to more than 300 even I had stopped creating new requests from JMeter. Then it took quite some time to decrease to 30 or so.
My VS2017 gave me the following information when I attached it to the process,

Making the function Sync solves the problem on my local computer, but it still happens when I deploy the app onto the Azure.
Function1.cs
``` c#
public class Function1
{
[FunctionName(nameof(Function1))]
public static void Run(
[HttpTrigger("POST")]string body,
[Queue("myqueue")]ICollector queue,
[Blob("mycontainer/{rand-guid}")]CloudBlockBlob cbc,
ILogger logger
)
{
try
{
logger.LogWarning(new EventId(-1, "FunctionStart"), $"{body?.Length}");

if (body != null)
{
try
{
cbc.UploadTextAsync(body).Wait();
}
finally
{
queue.Add(cbc.Name);
}
}

logger.LogWarning(new EventId(-1, "FunctionEnd"), $"{body?.Length}");
}
catch (Exception gex)
{
logger.LogError(new EventId(-1, "FunctionError"), gex, body);
}
}
}
```

The same thing recurs after I replace the `await cbc.UploadTextAsync(body)` with `await Task.Delay(1000)`.
So, my question is : `maxConcurrentRequests` is not capable of limiting the thread count? How does it work exactly?