photoshop and synfig size don't match

I am trying to make a gif for facebook cover photo 851X315. I created a base jpg in photoshop and imported to synfig. Whatever settings I use in canvas properties to get the right gif output at the same size, I fail. Either the original is too big for the canvas or when it matches the output is too big for facebook. the Xres and Yres don’t make any difference in this respect. The documentation on canvas properties is of no help. I would appreciate your insight. :frowning:

I applied a workaround by using the image’s size handler to change the dimensions to fit the canvas, but I wonder why that was needed in the first place.

Press F8 and resize canvas