Bad sizing - Rab Hunza Stretch Mid Gaiter - Men's

I wear a size 12 shoe, and bought size large. Bought these to keep rain from going into my shoe from the leg when I am wearing shorts and goretex hikers. Size on boot is great but size around ankle is terrible. These must be meant for people wearing thick socks and those that have fat leg cankles because I cannot cinch it tight enough.