It is true that such feet can and should be used with the very small zippers that are encountered in dressmaking, but the zippers that we use in canvas work are quite large.
Nothing is gained here by the use of the half size foot.
Indeed, feeding capacity and stitch quality will be degraded if such feet are used. This stitch closes the sleeve right behind the rope. Zipper feet are also used to make and install welting. There are, however, special presser feet with tunnels for installing welting. These feet are optional for our bigger machines.