How often do leather hiking boots shrink?

When you remove the oils from leather, the leather constricts. I always buy my boots a half-size larger than a close fit, then always wear two pair of socks. I never have shrinkage in synthetic or leather boots. The best leather treatment that I ever found is Timberland Waximum Waxed Leather Protector, although I have tried mink oil, Nikwax, and silicone treatments.