How to correctly catch the CollapsingToolbarLayout event?

Question

Android

There is the following layout:

<android.support.design.widget.AppBarLayout
        android:id="@+id/app_bar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:fitsSystemWindows="true"
        android:theme="@style/AppTheme.AppBarOverlay"
        app:elevation="0dp">

        <android.support.design.widget.CollapsingToolbarLayout
            android:id="@+id/toolbarLayout"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:fitsSystemWindows="true"
            app:contentScrim="?attr/colorPrimary"
            app:layout_scrollFlags="scroll|exitUntilCollapsed"
            app:statusBarScrim="?attr/colorPrimaryDark">

            <com.daimajia.slider.library.SliderLayout
                android:id="@+id/slider"
                android:layout_width="match_parent"
                android:layout_height="300dp"
                android:background="@android:color/white"
                android:fitsSystemWindows="true"
                app:layout_collapseMode="parallax"/>

            <android.support.v7.widget.Toolbar
                android:id="@+id/toolbar"
                android:layout_width="match_parent"
                android:layout_height="?attr/actionBarSize"
                app:layout_collapseMode="pin"
                app:popupTheme="@style/AppTheme.PopupOverlay"/>

        </android.support.design.widget.CollapsingToolbarLayout>

    </android.support.design.widget.AppBarLayout>

I want to make the icons in the STATUS BAR dark when scrolling, at the moment of changing the transparency of the content from the CollapsingToolbarLayout.
Did it like this:

AppBarLayout appBarLayout = (AppBarLayout) findViewById(R.id.app_bar);
        appBarLayout.addOnOffsetChangedListener(new AppBarLayout.OnOffsetChangedListener()
        {
            @Override
            @TargetApi(Build.VERSION_CODES.M)
            public void onOffsetChanged(AppBarLayout appBarLayout, int verticalOffset) {
                int toolbarHeight = toolbar.getHeight();
                int appBarHeight = appBarLayout.getHeight();

                int flagLight = View.SYSTEM_UI_FLAG_LIGHT_STATUS_BAR;
                int flag = appBarLayout.getSystemUiVisibility();

                if (appBarHeight + verticalOffset > 2 * toolbarHeight) {
                    if ((flag ^ flagLight) == flagLight) {
                        appBarLayout.setSystemUiVisibility(flag | flagLight);
                    }
                    return;
                }

                if ((flag & flagLight) == flagLight) {
                    appBarLayout.setSystemUiVisibility(flag ^ flagLight);
                }
            }
        });

But this method does not work exactly, i.e. icons become dark earlier than necessary (see gif)