This is my second year of training five pear and apple trees to a 4 tier cordon. So far everyone is complying and responding well to growing in two dimensions. Every week I make sure to bend down new growth and tie it down. Some of my branches are already reaching the full length of how long horizontally I'll let them grow to. Once all 4 tiers are established it's just a matter of pruning any undesirable growth from there on.