With your style being so bold and contemporary, I think you definitely can go larger on the vase, and I would reconsider whether those orchids are the right flower to use. Given the height that you have and no chandelier, you could go taller, more upright, so it can be seen clearly around th chair backs. If you want to use orchids, maybe something more like how they grow so the stems are taller.

Or maybe something more contemporary looking like calla lilies

Or an arrangement of several different flowers that can give height and interest.

You didn't ask, but I'll comment anyway...looking at your room, I think I'd move the flanking pictures closer to the middle one to make more of a grouping as they coordinate nicely.

Take a look at the arrangements in the link below. Since Orchid stems are tall, I wouldn't use a tall vase. Look at the 3rd picture, top row. I love how the container is short. I think it adds more of a punch to the arrangement.

Just because your chair's are high, even the smallest vase/container will be seen.

I definitely wouldn't arrange them like the picture above. For a more realistic look, the stems need to stand upright with a small bend at the top where the flowers drape down.

Three matching, medium size decorative containers (not vases) arranged in a circle sitting on a tray would look great!

Here is a link that might be useful: Silk Orchid arrangements

Is this for a dinner party or just a decorative element for non-table-use times. If for a dinner party keep in mind the guests being able to see one another.

Annie is right about the pictures--too far separated....

I've always preferred a shorter vase/container, but maybe it's because I equate 'large' with hotel lobby, wedding table, more of a commercial look than residential. I've only used one tall vase, but it's because I've also used tall, heavy candlesticks on the same table. But again, it's what appeals to you.