Android : Text over image with matching relative positioning

i'm in stuck. The problem is how to place text on a static image and keep position depends on it between different screen resolutions. To achive this i've tried the layout above:

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@android:color/black"
    android:padding="@dimen/default_view_padding">

    <ImageView
        android:id="@+id/iv_background"
        android:layout_width="500dp"
        android:adjustViewBounds="true"
        android:layout_height="900dp"
        android:layout_centerInParent="true"
        android:src="@drawable/example"/>

    <TextView
        android:layout_alignLeft="@id/iv_background"
        android:layout_alignStart="@id/iv_background"
        android:layout_alignEnd="@id/iv_background"
        android:layout_alignRight="@id/iv_background"
        android:layout_alignTop="@id/iv_background"
        android:layout_width="wrap_content"
        android:layout_marginTop="190dp"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:gravity="center"
        android:text="Dummy text string"/>

</RelativeLayout>

But on different screens it looks differently. So, by example, screenshots. The static image background, the view with text on nexus5, on nexus7. As you can see, a text placed on different places over image. I doesn't know why is it happend, becouse i'm using dp and relative layout.

I tried wrap_content/match_parent on image sizes, without ajust view bounds etc. And it haven't help. Ty for answers