This morning somehow I knew I was too weak to do well at Hatfield so went to Goodwin for a 'technique' session. I felt tired throughout and struggled to keep either pace or form. Such is back-to-back exercise. I kept thinking about a high elbow but whenever I took a sneeky look I wasn't convinced that it looked 'high'. My forearm certainly didn't seem to be vertical!
On the walk home it started to dawn on me what all the business I'd heard about 'reaching over a barrel' meant. It's all about the hard-to-achieve action of shoulder and upper arm up and forwards. Just keeping the elbow high still allows the forearm to trail when looking from the side. What's needed isn't so much a high elbow as a forwards elbow. This involves some abduction of the shoulder which can be reversed to adduction to help drive the body over the arm and thus forwards.
Thinking about this, trying to achieve a force-generating vertical forearm with a non-abducted shoulder requires substantial input from muscles crossing the elbow to generate tension. If the shoulder is abducted the forearm is largely pushed backwards which may well be more resilient.