I can't tell you how many times I've seen arcanists accidentally wipe a group upon entering and summoning a pet due to Ramuh-Ex's apparent aggro range.

What's happening is this:

Enter, stand in the circle. Don't move a muscle. Summon your pet from where you're standing (as you usually would do upon entering an instance), and it will spawn in a number of different possible locations... one of these possible locations is ahead of the group, close enough to the boss to aggro him. Because pets aggro and because Ramuh's first attack is an AoE and you are standing on the water, it will likely be an instant wipe.

You CAN avoid this issue by standing back at the edge of the arena before summoning, but I think a simple aggro range fix might completely remove this annoying issue without actually affecting the fight in any way.

Again, I believe this ONLY happens in Ramuh (extreme). Perhaps Ramuh hard's aggro radius is smaller? Haven't tested it extensively.