Ripple effect drawable is distorted when applied over 9patch background

I have a 9 patch drawable which I want to use as a background on a view. I want the view to show a ripple effect that follows the outline of a 9 patch when the view is clicked. Here's my activity, layout, and drawable code.

MainActivity.kt:

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val click = findViewById<ConstraintLayout>(R.id.container)
        click.setOnClickListener { Toast.makeText(this, "Clicked", Toast.LENGTH_SHORT).show() }
    }
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.antonc.testapp.MainActivity">

    <android.support.constraint.ConstraintLayout
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:paddingBottom="8dp"
        android:paddingStart="8dp"
        android:paddingEnd="8dp"
        android:paddingTop="16dp"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        android:background="@drawable/tooltip_background"
        android:backgroundTint="#2681d8"
        tools:layout_editor_absoluteX="8dp">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="Hello test test !!!"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintHorizontal_bias="0.0"
            />

    </android.support.constraint.ConstraintLayout>

</android.support.constraint.ConstraintLayout>

tooltip_background.xml:

<?xml version="1.0" encoding="utf-8"?>
    <ripple xmlns:android="http://schemas.android.com/apk/res/android"
android:color="#33000000">
    <item android:drawable="@drawable/tooltip_left_top"/>
    <item android:id="@android:id/mask" android:drawable="@drawable/tooltip_left_top"/>
</ripple>

tooltip_left_top.9.png:

But when I click on it, the ripple drawable is very distorted, as if it's stretched to the view size without observing the stretch rules of 9 patch. How should I configure the ripple to make it be the same as the background?:

from Ripple effect drawable is distorted when applied over 9patch background