100% of the time when looking for dupes on the mobile site I open a new tab to find the dupe. By the time I'm ready to vote I already know which question I'll select: I've reviewed it and don't need the preview.
However, especially if the post is long, after pasting the link this generally involves a ton of swiping to get past the preview (which I am not interested in) and down to the vote button.
Also you can't just blindly swipe to the bottom, as you can overshoot the preview window and pass the button.
To this end I would like to see the vote button also appear at the top of the preview window, at least on the mobile site, to help cut down on the general misery that is mobile web browsing. There is value to keeping it at the bottom which is why I don't think this is necessarily appropriate for the desktop site.