I think the miror is little too large especially too high. Since it is very low and close from the faucet, it will get dirty very easily with splashes of water. Probably a smaller size and higher positionned would have been a better match according to me.

Wouldn't it be better in a horizontal position?

This may be wider than your sink below but you can try. I think it will still look a little oversized. I guess a size smaller would look better proportionned.

Thanks it confirmed my intuition!