I just did this yesterday, cut WOF then added extra WOF and seamed it diagonally worked fine and the eye doesn't stop at the seam.
BUT I made a huge boo boo when sewing on my binding, joining the beginning and end of my binding ...never made this mistake b4, felt confident, cut and 'snapped it' together .. oh sh*!, the raw edges were on the ouside of the seam! Buggers. Gratefully it was a wide satin binding in a pkg, so it wasn't a standard narrow seam. I had to use a decorative stitch to stitch down and 'hide ?' the raw edges, making a triangle shape in the satin. The raw edges are hidden but not the mistake, darn it.
The quilt is for a 4yo granddaughter who will never know that it isn't supposed to look like that. but I still feel guilty about making this mistake, and pretty duh dumb too.
I'm thinking of writing her name in the triangle in pigma pen but afraid it will bleed/spread on the satin.
warm quilt hugs, sue in CA