Having done much of my flying from a RNoAF heli base with a certain JHC presence each year , I have some insight into this.
Yes, you will feel wake vortex from a medium helo like a Sea King or Puma, and was taught, and indeed felt that you should stay above the helos approach path if landing closer behind than say 3-4 miles.
From the tower I've seen a Grob get chucked around violently forcing a go-around when spacing up close behind a Sea King. Made him more aware about what "caution wake turbulence" actually means.
Smaller helos like the 412, Lynx etc not that bad, but you do feel their wake more than what their tonnage would imply. You will be affected if you turn in say 1-2 miles behind a 412, but not in such a way that it becomes dangerous IMHO.