Can the 6.25 in. x 6.25 in. PVC Base Vent Pipe Flashing with Adjustable Rubber Collar work with a flashing with a six inch opening?

This rain collar is not designed to work with a flashing with a 6 inch opening.

This rain collar is not designed to work with a flashing with a 6 inch opening. We do not suggest using with a 6 inch opening metal roof flashing as a temporary fix.