Change popular posts image list size?

At this time, setting it to a non-square size is not supported.

You can adjust the size via the jetpack_top_posts_widget_image_options filter like

function adjust_jetpack_top_posts_size( $options ) {
$options[ 'avatar_size' ] = 190; // 190 x 190 image size.
return $options;
}
add_filter( 'jetpack_top_posts_widget_image_options', 'adjust_jetpack_top_posts_size' );

Cheers!

Darn!!

Thanks so much for that help though! I hope it’s supported and perhaps even a future setting in the widget :).