functions.php

/**
 * Grid Loop Query Arguments
 *
 * @author Bill Erickson
 * @link http://www.billerickson.net/a-better-and-easier-grid-loop/
 *
 * @param object $query
 * @return null
 */
function be_grid_loop_query_args( $query ) {
	$grid_args = be_grid_loop_pagination( $query );
	if( $query->is_main_query() && !is_admin() && $grid_args ) {

		// All Grid Loops
		$query->set( 'orderby', 'meta_value' );
		$query->set( 'meta_key', 'sort_plek' );
		$query->set( 'order', 'DESC' );

		// First Page
		$page = $query->query_vars['paged'];
		if( ! $page ) {
			$query->set( 'posts_per_page', ( $grid_args['features_on_front'] + $grid_args['teasers_on_front'] ) );

		// Other Pages
		} else {
			$query->set( 'posts_per_page', ( $grid_args['features_inside'] + $grid_args['teasers_inside'] ) );
			$query->set( 'offset', ( $grid_args['features_on_front'] + $grid_args['teasers_on_front'] ) + ( $grid_args['features_inside'] + $grid_args['teasers_inside'] ) * ( $page - 2 ) );
			// Offset is posts on first page + posts on internal pages * ( current page - 2 )
		}

	}
}
add_action( 'pre_get_posts', 'be_grid_loop_query_args' );