How to show a message if feature points are less?

I am trying to build an app using ARKit with persistence.So I would like to show a message if they did not get enough feature points.

Code (CSharp):

1. if(aRCamera.trackingReason==ARTrackingStateReason.ARTrackingStateReasonInsufficientFeatures)
2.         {
3.             SaveText("Less Feature Points");
4.  
5.         }
6.  

The above code works only if we hide the camera.But I want is like it should support enough feature points so that next time just scanning in a casual way should create a persistence experience.I think enough feature points would help.So i dint get enough feature points in my scan I need to show a message.So the feature points for the tracking the desired path/particluar space has to be 90% anything less than that value show a toast.Any luck?