Pruning hedge - Cotoneaster franchetii

I know this is the 'tree' sub-forum, but seemed best match.

I have this year planted a 75m run of Cotoneaster franchetii - I used Mycorrhizal Fungi on roots, imported new soil for the 75m trench, and water daily when dry, and feed weekly with seaweed feed. So given them as good as I could.

Went in as 75cm plants in early and are now well over 1.5m .. but of course curved stems, not vertical growth

They are going well ... flowering now over, and berries are out ... how much should I prune in first year ... do I just take around a 1/3rd off the new growth on the main leaders.

Looking to get them to bush out before I aim to get to final height.