Is the wall it is going on higher or wider?
I would put the grooves in the longer direction. Depends which way you want the eye to follow.
Will water and debris get caught up in the grooves if you install it as pictured? If so, I would vote up and down as well.
I was going to suggest east/west like you pictured it just because I think as the water moves up and down it'll look very natural.
Pools require a regular cleaning / brushing schedule - you are going to hate that tile in a year, no matter what direction you put them....
If you follow TFP's water balanced guidelines and make a habit of hand cleaning that pretty tile with a soft brush you should be okay. It will be worth it as that is so pretty!!
The TF-100 has more of the regents we use the most. I will also suggest you get it from the link in my siggy below as I KNOW their regents are fresh! We have seen many that come from Amazon being outdated
Thank you! ?That tile will be fine just be aware its gonna need some upkeep. Be proactive and scrub it even when it looks clean