As with all issues viticulture-related there are multiple theories and the number of clips required per vine is no exception. We recommend that C clips are placed centrally between vines in the trellis bay though not adjacent to the trellis post. This should tension the foliage wires sufficiently, but allow enough slack should further (vertical) shoot positioning be required after clipping. Some growers use two clips per bay on lower wires and three per bay on top wires. Allow a minimum of one clip per vine.
Bingo! You should now have perfectly vertical ‘jail bar’ shoots throughout your canopy.