Change the size of the font in the signature field
Padding is added above and below the signature image, but not on the sides. This makes it so the signature image is almost 1/2 the height of the signature box. Please take away the padding, it would work so much better.
Emily Gould commented
Uploaded an image signature is tiny on the document compared to others that just use the default text. Uploaded signature needs to fill the signature box.