I don’t think it should matter so long as there are enough leaves and light for the clusters to ripen. In wine grape growing there are a lot of different trellis styles and pruning styles. Some have a short trunk and then have the fruiting canes about 3 feet off the ground with all the shoots and leaves growing up. Others do the opposite and have a much longer trunk and have the grape clusters up a the top with the shoots and leaves hanging down below.
Here in Virginia, where the wine growing industry is relatively young, the cutting edge guys have been experimenting with vine spacing, row spacing, trellis and pruning styles, etc and a lot of what was standard practice 20 years ago (based on California or France) has been scrapped and updated based on experimentation and lessons learned. I say all of that as an intro to TheNiceGuy’s comment above regarding a “formula for vine length and efficient fruit growth”.
I don’t know the exact formula, but if I remember correctly, it has to do with the number of leaves to fully ripen the clusters of grapes. It’s something like 12 leaves per cluster which works out to something like 3 or 4 feet of shoot length. Anything less than that and the grapes won’t fully ripen, and anything more than that is overkill and will throw the vines out of balance for the following year. (Balance has to do with keeping the vines in that sweet spot where they grow just enough to ripen the grapes, but not enough to store too much energy in the plant/roots which would cause excessive growth the following year leading more pruning and more time per vine.)
For the wine growers, knowing the optimal shoot height (or trellis height) is important because they can calculate their row spacing based on the height of the vines and the amount of light vs. shadows (from the adjacent row) that the vines receive. This allows them to pack in as many vines per acre as possible while still allowing the grapes to fully ripen while keeping the vines “balanced” and keeping vegetative growth in check. For home fruit growers, it’s not nearly as important, but the point is, beyond certain shoot length/number of leaves, it’s overkill
This was a very long winded way of saying that so long as there are enough leaves (exposed to the sun) to ripen each cluster, I don’t think it matters if you grow up, down or sideways.
Here’s an article on different trellis types. It’s for wine growers, but it applies to any type of grape: