I lay W&N pieces overlapping just a little bit and trim both layers. Remove the slivers & butt the big pieces together. Lay the interfacing over the joint and press. I use steam and an applique sheet (just because I have one) but you could use a scrap of muslin to keep the glue off your iron. THEN - I take it to my machine. Turn it over so that the fusible is on the bottom and zig-zag the joint. I use as wide a zig-zag as my machine does and a fairly open length. I like to reinforce the fusible - kinda like the fusible is holding everything together so you CAN sew it together.
I use this method to put ALL my scrap W&N together into a usable size, I don't like to throw it away.