Change thumbnail size on public directory detail page
I believe that thumbnail size is set by CSS (at least it is in the backend), the actual contact image should be whatever size you uploaded the image at originally. Perhaps you can adjust the CSS to display those contact images at your desired size.

Based on your page, you could use:

.content img {
    width: auto;
    height: auto;
}


To set it to it's native size. You could alternatively used specific values (height: 200px; width: auto;) to be a little more uniform across different contact results.