Index: src/wp-content/themes/twentyfifteen/inc/customizer.php
===================================================================
--- src/wp-content/themes/twentyfifteen/inc/customizer.php	(revision 39151)
+++ src/wp-content/themes/twentyfifteen/inc/customizer.php	(working copy)
@@ -17,6 +17,9 @@
 function twentyfifteen_customize_register( $wp_customize ) {
 	$color_scheme = twentyfifteen_get_color_scheme();
 
+	$wp_customize->remove_control('background_preset');
+	$wp_customize->remove_control('background_size');
+
 	$wp_customize->get_setting( 'blogname' )->transport        = 'postMessage';
 	$wp_customize->get_setting( 'blogdescription' )->transport = 'postMessage';
 
Index: src/wp-content/themes/twentyseventeen/style.css
===================================================================
--- src/wp-content/themes/twentyseventeen/style.css	(revision 39151)
+++ src/wp-content/themes/twentyseventeen/style.css	(working copy)
@@ -3901,13 +3901,6 @@
 	}
 }
 
-@media screen and ( min-width: 55em ) {
-
-	.panel-image {
-		background-attachment: fixed;
-	}
-}
-
 @media screen and ( min-width: 67em ) {
 
 	/* Layout */
@@ -3921,6 +3914,11 @@
 		margin-left: 0;
 	}
 
+	/* Front Page */
+	.panel-image {
+		background-attachment: fixed;
+	}
+
 	/* Sticky posts */
 
 	.sticky .icon-thumb-tack {
@@ -3958,6 +3956,19 @@
 	}
 }
 
+/* Override fixed backgrounds on iPad Pro */
+@media screen and ( min-device-width : 64em ) and ( max-device-width : 64em ) and ( min-device-height : 85.375em ) and ( max-device-height : 85.375em ) and ( min-width: 64em ) and ( max-width: 64em ) {
+	.panel-image {
+		background-attachment: scroll;
+	}
+}
+
+@media screen and ( min-device-width : 64em ) and ( max-device-width : 64em ) and ( min-device-height : 85.375em ) and ( max-device-height : 85.375em ) and ( min-width: 85.375em ) and ( max-width: 85.375em ) {
+	.panel-image {
+		background-attachment: scroll;
+	}
+}
+
 @media screen and ( min-width: 79em ) {
 
 	.has-sidebar .entry-content blockquote.alignleft {