Option toBack in Camera Preview plugin seems ignored

Hi folks,

i want to use camera preview plugin with the option ‘toBack’ but it seems not work on capacitor.

// camera options (Size and location). In the following example, the preview uses the 
rear camera and display the preview in the back of the webview
const cameraPreviewOpts: CameraPreviewOptions = {
  x: 0,
  y: 0,
  width: window.screen.width,
  height: window.screen.height,
  camera: 'rear',
  tapPhoto: true,
  previewDrag: true,
  toBack: true,
  alpha: 1
}

// start camera
this.cameraPreview.startCamera(cameraPreviewOpts).then(
  (res) => {
    console.log(res)
  },
  (err) => {
    console.log(err)
  });

Here is my environment

Ionic:

   ionic (Ionic CLI)             : 4.12.0 (/usr/local/lib/node_modules/ionic)
   Ionic Framework               : @ionic/angular 4.4.2
   @angular-devkit/build-angular : 0.13.9
   @angular-devkit/schematics    : 7.3.9
   @angular/cli                  : 7.3.9
   @ionic/angular-toolkit        : 1.5.1

Cordova:

   cordova (Cordova CLI) : 9.0.0 (cordova-lib@9.0.1)
   Cordova Platforms     : none
   Cordova Plugins       : cordova-plugin-ionic-keyboard 2.1.3, cordova-plugin-ionic-webview 4.0.1, (and 6 other plugins)

System:

   Android SDK Tools : 26.1.1 (/Users/ihsanberahim/Library/Android/sdk)
   ios-deploy        : 1.9.4
   NodeJS            : v8.16.0 (/usr/local/Cellar/node@8/8.16.0/bin/node)
   npm               : 6.9.0
   OS                : macOS Mojave
   Xcode             : Xcode 10.2.1 Build version 10E1001