Twilio video virtual background processor tuning for sharp outlines

Question

I'am using twilio video processors to add virtual backgrounds to my video tracks. The problem is that the outlines of the speaking person are not sharp, they are randomly mixed with the virtual background. Sometimes a entire part like the hand is being hidden by the backgound, especially whe the person is moving. Here are my setting when starting the virtual effect :

 this.virtualP = new VideoProcessors.VirtualBackgroundProcessor({
          assetsPath: '/assets/video-processors/',
          backgroundImage: img,
          fitType: VideoProcessors.ImageFit.Fill,
          maskBlurRadius: 10 
        });

I tried playing with the maskBlurRadius but did not get any real improvement.

Any hints ? Thanks