KiloKilo,
I had the same experience on shift a few years ago. A Medium turbo-prop 18NM behind a B767 on a high speed descent through his level. The turbo-prop reported encountering "Severe Wake Turbulence" and ever since then I've past a caution whenever I thought that a smaller aircraft was going to transit the wake turbulence of a heavy, even if the distance between the aircraft was in excess of the Wake Turbulence Separation Standard behind.
Interesting that on one occasion when I did this, one of my colleagues turned to me and said... "you don't know your Wake Turbulence Standards" because I'd chosen to pass a caution when the distance between the aircraft was in excess of the Wake Turbulence Standard in MATS.
I thought we were in the business of saving people's lives, regardless, but not in spite of, what is written in the books.