Xamarin forms iOS audio record metering not working

Question

I am trying to implement metering for my custom audio recorder for the iOS xamarin forms project. However after turning on metering and polling it, the value is always -160. I am using a physical device, iPhone X to test. Below is my recording code:

 public string Record(string filePath)
    {
        var audioSession = AVAudioSession.SharedInstance();
        var err = audioSession.SetCategory(AVAudioSessionCategory.PlayAndRecord);
        if (err != null)
        {
            Console.WriteLine("audioSession: {0}", err);
            return err.ToString();
        }
        err = audioSession.SetActive(true);
        if (err != null)
        {
            Console.WriteLine("audioSession: {0}", err);
            return err.ToString();
        }

        _url = NSUrl.FromFilename(filePath);
        //set up the NSObject Array of values that will be combined with the keys to make the NSDictionary
        NSObject[] values = new NSObject[]
        {
             NSNumber.FromFloat (44100.0f), //Sample Rate
             NSNumber.FromInt32 ((int)AudioFormatType.LinearPCM), //AVFormat
             NSNumber.FromInt32 (2), //Channels
             NSNumber.FromInt32 (16), //PCMBitDepth
             NSNumber.FromBoolean (false), //IsBigEndianKey
             NSNumber.FromBoolean (false) //IsFloatKey
        };


        //Set up the NSObject Array of keys that will be combined with the values to make the NSDictionary
        NSObject[] keys = new NSObject[]
        {
             AVAudioSettings.AVSampleRateKey,
             AVAudioSettings.AVFormatIDKey,
             AVAudioSettings.AVNumberOfChannelsKey,
             AVAudioSettings.AVLinearPCMBitDepthKey,
             AVAudioSettings.AVLinearPCMIsBigEndianKey,
             AVAudioSettings.AVLinearPCMIsFloatKey
        };

        //Set Settings with the Values and Keys to create the NSDictionary
        _settings = NSDictionary.FromObjectsAndKeys(values, keys);

        //Set recorder parameters
        _recorder = AVAudioRecorder.Create(_url, new AudioSettings(_settings), out _error);

        if (_error != null)
            return _error.ToString();

        //Set Recorder to Prepare To Record
        _recorder.MeteringEnabled = true;
        _recorder.PrepareToRecord();
        
        _recorder.Record();

        return "";
    }

Below is the code that i poll to log the metering info. It is being called from a threading timer event.

private void ShowMetering()
    {
        _recorder.UpdateMeters();
        Console.WriteLine($"metering:{_recorder.MeteringEnabled} peak power1: {_recorder.PeakPower(0)} avg power1: {_recorder.AveragePower(0)}");
    }